Nitrogen-containing alloy and method for producing phosphor using same

ABSTRACT

A method for industrially producing a phosphor with high performance, in particular, high brightness. Also disclosed is a nitrogen-containing alloy and an alloy powder useful for producing the high performance phosphor. The method for producing the phosphor includes heating a raw material for a phosphor in whole or in part comprising an alloy containing two or more different metal elements under a nitrogen-containing atmosphere and heating the raw material for a phosphor under conditions such that the temperature change per minute is 50° C. or lower. Using an alloy as all or part of the raw material constituting the phosphor precursor, it is possible to suppress the rapid progression of nitridation during heat treatment and industrially produce a phosphor with high performance, in particular, high brightness.

FIELD OF THE INVENTION

The present invention relates to a nitrogen-containing alloy as astarting material for producing a phosphor composed of a nitride matrixor an oxynitride matrix and also relates to a method for producing aphosphor composed of a nitride matrix or an oxynitride matrix using thenitrogen-containing alloy as a starting material.

BACKGROUND OF THE INVENTION

Phosphors are used in such apparatuses as fluorescent lights, vacuumfluorescent displays (VFD), field emission displays (FED), plasmadisplay panels (PDP), cathode-ray tubes (CRT), and white light-emittingdiodes (LED). In any of these applications, a phosphor requires thesupply of excitation energy for emitting light. After being excited by ahigh-energy source that emits vacuum ultraviolet light, ultravioletlight, visible light, electron beams or the like, such a phosphor emitsultraviolet light, visible light, or infrared light. However, there hasbeen a problem that the long-term exposure of a phosphor to such anenergy source may result in the deterioration of brightness.

In response to this, many novel ternary or more complex nitrides haverecently been developed as alternatives to known phosphors, such assilicate, phosphate, aluminate, borate, sulfide, and oxysulfidephosphors. In particular, recently developed silicon nitride-basedmulticomponent nitrides and oxynitrides exhibit excellentcharacteristics as phosphors.

Patent Document 1 discloses phosphors represented by the general formulaM_(x)Si_(y)N_(z):Eu (M is one or more alkaline earth metal elementsselected from the group consisting of Ca, Sr, and Ba, whereas x, y, andz are numbers that satisfy the relationship expressed as z=2/3x+4/3y).Such phosphors are synthesized by nitridation of alkaline earth metalelements and then mixing the obtained alkaline earth metal elementnitrides with silicon nitride or by heating alkali earth metal imidesand silicon imides as raw materials under nitrogen or argon flow. Bothsynthetic methods require alkaline earth metal element nitridessusceptible to air and moisture as raw materials, and thus areunsuitable for industrial manufacturing.

Patent Document 2 discloses oxynitride phosphors having an oxynitriderepresented by the formula M₁₆Si₁₅O₆N₃₂:Eu and oxynitride phosphorshaving SiAlON structures each represented by the formula MSiAl₂O₃N₂:Eu,M₁₃Si₁₈Al₁₂O₁₈N₃₆:Eu, MSi₅Al₂ON₉:Eu, or M₃Si₅AlON₁₀:Eu. It states that,particularly in the case where M was Sr, heating the mixture of SrCO₃,AlN, and Si₃N₄ at a ratio of 1:2:1 in a reducing atmosphere(hydrogen-containing nitrogen atmosphere) resulted in the formation ofSrSiAl₂O₃N₂:Eu²⁺.

This approach provides oxynitride phosphors only and thus does notprovide phosphors based on nitrides free from oxygen.

Furthermore, raw materials of the nitride or oxynitride phosphorsdescribed above have low reactivity in a powder form. Thus, to promotethe solid state reaction between the particles of the raw materialsduring firing, the raw materials should be heated with the maximumcontact area between particles thereof. As a result, the synthesizedphosphor is in the state of being compacted at high temperatures, inother words, in the state of a very hard sintered body. Such a sinteredbody should be pulverized into fine particles, which is a form suitablefor its intended purposes as a phosphor. However, milling such a hardsintered body of a phosphor for a long period of time with tremendousenergy in an ordinary mechanical method, for example, with the use of ajaw crusher or a ball mill, would result in the generation of manydefects in the matrix crystal of the phosphor and thereby lead to thesignificant deterioration of the light emission intensity.

Meanwhile, the patent documents state that, in the production of suchnitride or oxynitride phosphors, alkaline earth metal element nitridessuch as calcium nitride (Ca₃N₂) and strontium nitride (Sr₃N₂) arepreferably used. However, in general, divalent metal nitrides are likelyto react with water to produce hydroxides and thus unstable under awater-containing atmosphere. This tendency is marked especially in theparticles of Sr₃N₂ and metallic Sr, so these kinds of nitrides are verydifficult to handle.

For the reasons described above, novel raw materials of phosphors andmethods for producing them are demanded.

A method for producing a nitride phosphor using a metal as a startingmaterial has recently been reported in Patent Document 3. PatentDocument 3 discloses an example of a method for producing an aluminumnitride-based phosphor and describes that a transition elements, a rareearth element, aluminum, and an alloy thereof can be used as thestarting materials. However, this patent document describes no examplein which such an alloy is actually used as a starting material butdescribes that metallic Al is used as an Al source. This method uses acombustion synthesis technique in which a starting material is rapidlyheated to a high temperature (3,000 K) by igniting the starting materialand therefore is significantly different from a method according to thepresent invention. It is probably difficult to produce ahigh-performance phosphor by this method. More specifically, the methodin which the starting materials are instantly heated to a temperature ashigh as 3,000 K has difficulties in distributing activator elementsevenly and thus cannot easily provide a high-performance phosphor. Thisdocument describes no nitride phosphor containing an alkaline-earthelement obtained from the alloy or no nitride phosphor containingsilicon.

-   Patent Document 1: PCT Japanese Translation Patent Publication No.    2003-515665-   Patent Document 2: Japanese Unexamined Patent Application    Publication No. 2003-206481-   Patent Document 3: Japanese Unexamined Patent Application    Publication No. 2005-54182

The inventors have conducted studies and found that in the case of theproduction of a phosphor composed of a nitride matrix or an oxynitridematrix from an alloy as a raw material, a nitridation reaction proceedsrapidly during heating, so that the generated heat may cause melting andphase separation of the raw material and decomposition of the resultingnitride, thereby degrading the properties of a phosphor produced. Theinventors also found that in particular, in the case where a largeamount of the raw material is heat-treated at one time or the packingdensity of the raw material is increased in order to increase theproductivity, a phosphor is not produced in some cases.

SUMMARY OF INVENTION

In consideration of the foregoing problems, the present invention hasbeen accomplished. It is an object of the present invention to provide amethod for industrially producing a phosphor with high performance, inparticular, high brightness. It is another object of the presentinvention to provide a phosphor prepared by the method for producing aphosphor, a phosphor-containing composition containing the phosphor, alight-emitting device containing the phosphor, an image displayincluding the light-emitting device, and a lighting system including thelight-emitting device.

It is another object of the present invention to provide anitrogen-containing alloy, and an alloy powder, which can be used forthe method for producing a phosphor.

In consideration of the foregoing problems, the inventors have conductedintensive studies on a method for producing a phosphor and found that inthe case where a phosphor is produced with an alloy containing two ormore metal elements that will constitute the phosphor (hereinafter, alsoreferred to as an “alloy for a phosphor precursor”), the alloy servingas the whole or part of a raw material, the control of a change intemperature during the heat treatment within a predetermined range in astep of heating the raw material for the phosphor results in an increasethe amount of the raw material capable of being heated at one time.

The gist of the present invention will be described in items (1) to (33)below.

(1) A method for producing a phosphor includes a step of heating a rawmaterial for the phosphor under a nitrogen-containing atmosphere, inwhich an alloy containing two or more different metal elementsconstituting the phosphor (hereinafter, referred to as an “alloy for aphosphor precursor”) is used as the whole or part of the raw materialfor the phosphor, and in the heating step, the heating is performedunder conditions such that the temperature change per minute in thetemperature range from a temperature 100° C. lower than the meltingpoint of the alloy for a phosphor precursor to a temperature 30° C.lower than the melting point of the alloy for a phosphor precursor is50° C. or lower.

(2) The method for producing a phosphor described in item (1) satisfiesat least one of requirements 1) to 4):

1) the whole or part of the alloy for a phosphor precursor is anitrogen-containing alloy having a total content of metal elements of97% by weight or less;

2) the heating rate is set at 9° C./min or less in the temperature rangefrom a temperature 100° C. lower than the melting point of the alloy fora phosphor precursor to a temperature 30° C. lower than the meltingpoint of the alloy for a phosphor precursor;

3) a nitride or an oxynitride containing one or two or more metalelements constituting the phosphor is used as the raw material for thephosphor together with the alloy for a phosphor precursor; and

4) a powder of the alloy for a phosphor precursor is used as the alloyfor a phosphor precursor, the powder having an angle of repose of 45° orless.

(3) The method for producing a phosphor described in (2) satisfies atleast requirements 1) and 2).

(4) The method for producing a phosphor described in (2) satisfies atleast requirements 2) and 3).

(5) In the method for producing a phosphor described in any one of items(1) to (4), in the heating step, the raw material for the phosphor isheated in a firing vessel, and the mass ratio of the raw material forthe phosphor to the firing vessel is 0.1 or more, the mass ratio beingrepresented by the following formula [A]:

(mass of raw material for phosphor)/{(mass of firing vessel)+(mass ofraw material for phosphor)}  [A].

(6) A method for producing a phosphor includes a step of heating a rawmaterial for the phosphor under a nitrogen-containing atmosphere, inwhich an alloy for a phosphor precursor is used as the whole or part ofthe raw material for the phosphor, and in which the method satisfies atleast one of requirements 1) to 4):

1) the whole or part of the alloy for a phosphor precursor is anitrogen-containing alloy having a total content of metal elements of97% by weight or less;

2) the heating rate is set at 9° C./min or less in the temperature rangefrom a temperature 100° C. lower than the melting point of the alloy fora phosphor precursor to a temperature 30° C. lower than the meltingpoint of the alloy for a phosphor precursor;

3) a nitride or an oxynitride containing one or two or more metalelements constituting the phosphor is used as the raw material for thephosphor together with the alloy for a phosphor precursor; and

4) a powder of the alloy for a phosphor precursor is used as the alloyfor a phosphor precursor, the powder having an angle of repose of 45° orless.

(7) In the method for producing a phosphor described in item (6), thenitrogen-containing alloy has a nitrogen content of 0.8% by weight to27% by weight.

(8) The method for producing a phosphor described in item (6) or (7)further includes a step (hereinafter, referred to as a “primarynitridation step”) of heating the alloy for a phosphor precursor under anitrogen-containing atmosphere to prepare the nitrogen-containing alloy.

(9) In the method for producing a phosphor described in any one of items(6) to (8), the nitrogen-containing alloy satisfies the formula [7]:

0.03≦NI/NP≦0.9  [7]

wherein in the formula [7],

NI represents the nitrogen content (% by weight) of thenitrogen-containing alloy, and

NP represents the nitrogen content (% by weight) of the phosphorproduced.

(10) In the method for producing a phosphor described in any one ofitems (6) to (9), the step (hereinafter, referred to as a “secondarynitridation step”) of heating the raw material for the phosphor, thewhole or part of the raw material being consisted of thenitrogen-containing alloy under the nitrogen-containing atmosphere isperformed at a temperature equal to or higher than a temperature 300° C.higher than the melting point of the nitrogen-containing alloy.

(11) The method for producing a phosphor described in any one of items(6) to (10) further includes a step of cooling the nitrogen-containingalloy to a temperature equal to or lower than a temperature 100° C.lower than the melting point of the nitrogen-containing alloy before thesecondary nitridation step.

(12) The method for producing a phosphor described in any one of items(6) to (11) further includes a step of milling the nitrogen-containingalloy before the secondary nitridation step.

(13) In the method for producing a phosphor described in any one ofitems (6) to (12), the alloy for a phosphor precursor has aweight-average median diameter D₅₀ of 100 μm or less.

(14) In the method for producing a phosphor described in any one ofitems (6) to (13), the raw material for the phosphor contains 1% byweight or more of a nitride or an oxynitride containing one or two ormore metal elements constituting the phosphor together with the alloyfor a phosphor precursor.

(15) In the method for producing a phosphor described in any one ofitems (6) to (14), the alloy for a phosphor precursor has a tap densityof 1.9 g/mL or more.

(16) A method for producing a phosphor includes a step of heating a rawmaterial for the phosphor under a nitrogen-containing atmosphere, inwhich an alloy for a phosphor precursor is used as the whole or part ofthe raw material for the phosphor, and in which the whole or part of thealloy for a phosphor precursor is a nitrogen-containing alloy having anitrogen content of 10% by weight or more.

(17) A method for producing a phosphor using an alloy for a phosphorprecursor includes:

(a) a melting step of melting at least one metal element and at leastone activating element M¹ constituting the phosphor to form a moltenalloy containing these elements;

(b) a size-reduction step of reducing the size of the molten alloy in aninert gas;

(c) a solidifying step of solidifying the molten alloy, the molten alloyhaving been reduced in size; and

(d) a firing step of firing the solidified alloy powder under a nitrogenatmosphere.

(18) In the method for producing a phosphor described in any one ofitems (1) to (17), the phosphor contains a tetravalent metal element M⁴containing at least Si and contains one or more metal elements otherthan Si.

(19) In the method for producing a phosphor described in item (18), thephosphor contains an activating element M¹, a divalent metal element M²,and the tetravalent metal element M⁴ containing at least Si.

(20) In the method for producing a phosphor described in item (19), thephosphor contains an alkaline-earth metal element serving as thedivalent metal element M².

(21) In the method for producing a phosphor described in item (19) or(20), the phosphor further contains a trivalent metal element M³.

(22) A nitrogen-containing alloy for producing a phosphor composed of anitride matrix or an oxynitride matrix as a host material includes atleast one metal element and at least one activating element M¹, in whichthe total content of metal elements is 97% by weight or less.

(23) In the nitrogen-containing alloy described in item (22), thenitrogen content is in the range of 0.8% by weight to 27% by weight.

(24) The nitrogen-containing alloy described in item (22) or (23)satisfies the formula [7]:

0.03≦NI/NP≦0.9  [7]

wherein in the formula [7],

NI represents the nitrogen content (% by weight) of thenitrogen-containing alloy, and

NP represents the nitrogen content (% by weight) of the phosphorproduced.

(25) The nitrogen-containing alloy described in any one of items (22) to(24) contains a tetravalent metal element M⁴ containing at least Si andcomprising one or more metal elements other than Si.

(26) The nitrogen-containing alloy described in item (25) contains anactivating element M¹, a divalent metal element M², and the tetravalentmetal element M⁴ containing at least Si.

(27) The nitrogen-containing alloy described in item (26) contains analkaline-earth metal element serving as the divalent metal element M².

(28) The nitrogen-containing alloy described in item (26) or (27)further contains a trivalent metal element M³.

(29) In the nitrogen-containing alloy described in any one of items (22)to (28), the activating element M¹ is at least one element selected fromthe group consisting of Cr, Mn, Fe, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er,Tm, and Yb.

(30) In the nitrogen-containing alloy described in item (28) or (29),the divalent metal element M² is at least one element selected from thegroup consisting of Mg, Ca, Sr, Ba, and Zn, the trivalent metal elementM³ is at least one element selected from the group consisting of Al, Ga,In, and Sc, and the tetravalent metal element M⁴ containing at least Siis at least one element selected from the group consisting of Si, Ge,Sn, Ti, Zr, and Hf.

(31) In the nitrogen-containing alloy described in item (30), 50% bymolar content or more of the divalent metal element M² is Ca and/or Sr,50% by molar content or more of the trivalent metal element M³ is Al,and 50% by molar content or more of the tetravalent metal element M⁴containing at least Si is Si.

(32) In the nitrogen-containing alloy described in item (30) or (31),the activating element M¹ contains Eu, the divalent metal element M²contains Ca and/or Sr, the trivalent metal element M³ contains Al, andthe tetravalent metal element M⁴ containing at least Si contains Si.

(33) A powder of an alloy serving as a raw material for a phosphorcontains at least one metal element, and at least one activating elementM¹, in which the alloy powder has an angle of repose of 45° or less.

The present invention makes it possible to suppress the rapid progressof a nitridation reaction in the heating step in producing the phosphorusing the alloy for a phosphor precursor as the whole or part of the rawmaterial, thereby industrially producing the phosphor with highperformance, in particular, high brightness.

The present invention also makes it possible to provide thenitrogen-containing alloy as an excellent raw material for the phosphorand the alloy powder with a low angle of repose.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view of a light-emitting deviceaccording to an embodiment of the present invention.

FIG. 2 a is a schematic cross-sectional view of a shell-shapedlight-emitting device according to an embodiment of the presentinvention, and FIG. 2 b is a schematic cross-sectional view of asurface-mount light-emitting device according to an embodiment of thepresent invention.

FIG. 3 is a schematic cross-sectional view of a lighting systemaccording to an embodiment of the present invention.

FIG. 4 is a schematic view of a gas atomizer suitable for a reduction insize of a molten alloy and the solidification of the molten alloy.

FIG. 5 is a chart showing the results of TG-DTA analysis of anitrogen-containing alloy prepared in Example 19.

FIG. 6 is a powder x-ray diffraction pattern of a nitrogen-containingalloy prepared in Example 11.

FIG. 7 is a powder x-ray diffraction pattern of a nitrogen-containingalloy prepared in Example 12.

FIG. 8 is a powder x-ray diffraction pattern of a nitrogen-containingalloy prepared in Example 13.

FIG. 9 is a powder x-ray diffraction pattern of a nitrogen-containingalloy prepared in Example 14.

FIG. 10 is a chart showing the results of TG-DTA analysis of an alloypowder before primary nitridation according to Comparative Example 1.

FIG. 11 is a powder x-ray diffraction pattern of a phosphor prepared inExample 12.

FIG. 12 is a powder x-ray diffraction pattern of a phosphor prepared inExample 13.

FIG. 13 is a chart showing the emission spectrum of a surface-mountlight-emitting device prepared in Example 20.

FIG. 14 is an optical photomicrograph of an alloy powder produced inExample 27.

FIG. 15 is an optical photomicrograph of an alloy powder produced inComparative Example 7.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention will be described in detailbelow. However, the present invention is not limited thereto, andvarious modifications may be made without departing from the scope ofthe invention.

In this specification, a numerical range expressed with the symbol “-”includes values which are each placed on the left or right of the symbol“-” and which each corresponds to a lower limit or an upper limit.

An alloy defined in this specification includes a solid solution, aeutectic, and an intermetallic compound, each being composed of two ormore metals, and a material containing a combination thereof. The alloymay contain a nonmetallic element.

[Method for Producing Phosphor]

A method for producing a phosphor according to the present invention(hereinafter, also referred to simply as a “production method of thepresent invention”) includes a step of heating a raw material for aphosphor under a nitrogen-containing atmosphere, in which an alloycontaining two or more metal elements constituting the phosphor(hereinafter, referred to as an “alloy for a phosphor precursor”) isused as the whole or part of the raw material for the phosphor.

A nitridation reaction is an exothermic reaction. Thus, in the casewhere a large amount of the raw material for a phosphor is subjected tonitridation by heating in the heating step at one time, a runawayreaction with a sharp exotherm occurs. The exotherm often causes theevaporation of part of constituent elements of the raw material for thephosphor and the fusion of particles of the alloy for a phosphorprecursor. The resulting phosphor has poor light emission properties orno phosphor is obtained, in some cases. Accordingly, in the productionmethod of the present invention, the control of the range of atemperature change during the heating step inhibits the rapid progressof the nitridation reaction even when the amount of the raw material forthe phosphor treated at one time is increased, thereby making itpossible to industrially produce high-performance phosphor.

It is important for the production method of the present invention thatin the heating step, a change in the temperature of the external wall ofa firing vessel into which the raw material for the phosphor is placedis small in a specific temperature range (i.e., it represents that arapid exothermal reaction does not occur). The specific temperaturerange above usually represents a temperature range from a temperature100° C. lower than the melting point of the alloy for a phosphorprecursor to a temperature 30° C. lower than the melting point.Preferably, the lower limit of the range is a temperature 150° C. lowerthan the melting point and more preferably a temperature 200° C. lowerthan the melting point. Preferably, the upper limit of the range is themelting point or lower and more preferably a temperature 100° C. higherthan the melting point.

The temperature change per minute in the heating step in the productionmethod of the present invention is usually 50° C. or lower, preferably30° C. or lower, more preferably 20° C. or lower, still more preferably10° C. or lower. An excessively large temperature change in the heatingstep is liable to cause a reduction in light emission properties of thephosphor. In some cases, a phosphor is not obtained. The lower limit ofthe range of the temperature change per minute is not particularlylimited but is usually 0.1° C. or higher from the viewpoint of achievinggood productivity. Furthermore, the temperature in the heating step maydecrease. The value of the “temperature change per minute in the heatingstep” represents the absolute value.

The “temperature change per minute in the heating step” is determined bymeasuring a temperature of the external wall of the firing vessel (athermometer is arranged at a height position approximately equal to halfthe height of the raw material for the phosphor placed therein.Hereinafter, this temperature is also referred to as a “side-walltemperature of the firing vessel”) at fixed time intervals with atungsten-rhenium alloy thermocouple, a platinum thermocouple,rhodium-platinum thermocouple, a radiation thermometer, or the like andcalculating the temperature change per minute from the formula [B] usingthe measurements:

Temperature change (° C./min)=temperature at time T min−temperature attime (T−1) min  [B].

In order to ensure that the temperature change represented by theformula [B] is not attributable to noise, the temperature is preferablymonitored at certain intervals or less. Specifically, the temperaturemeasurement interval is usually set at 30 seconds or less, preferably 20seconds or less, and more preferably 10 seconds or less. The lower limitof the temperature measurement interval is usually set at one second ormore.

In the formula [B], the temperature change per minute is specified.However, the temperature measurement interval is not particularlylimited. For example, a temperature change per 10 minutes is usually100° C. or lower, preferably 80° C. or lower, and more preferably 50° C.or lower. The lower limit of the range of the temperature change per 10minutes is not particularly limited but is usually 0.5° C. or higher.

The side-wall temperature of the firing vessel is approximately equal toa temperature in a furnace when a sharp exotherm does not occur in theheating step. Thus, in the case where the value of the formula [B] islarger than the value of a change in temperature in the furnace, thisusually means the occurrence of a rapid exothermic reaction.

The production method of the present invention is not particularlylimited as long as it satisfies the foregoing requirement. A method forcontrolling the temperature change in the heating step will be describedbelow.

A reduction in the amount of heat generated by a nitridation reactionper certain period of time (i.e., inhibition of the progress of a rapidnitridation reaction) can control the temperature change in the heatingstep within the range above. Specifically, ways satisfyingrequirements 1) to 4) are exemplified below. The production method ofthe present invention preferably satisfies at least one ofrequirements 1) to 4) described below. From the viewpoint of achievinggood productivity, the production method of the present inventionparticularly preferably satisfies at least requirement 1).

Details of requirements 1) to 4) will be described below.

1) The whole or part of the alloy for a phosphor precursor is anitrogen-containing alloy having a total content of metal elements of97% by weight or less.

2) The heating rate is set at 9° C./min or less in the temperature rangefrom a temperature 100° C. lower than the melting point of the alloy fora phosphor precursor to a temperature 30° C. lower than the meltingpoint of the alloy for a phosphor precursor.

3) A nitride or an oxynitride containing one or two or more metalelements constituting the phosphor is used as the raw material for thephosphor together with the alloy for a phosphor precursor.

4) A powder of the alloy for a phosphor precursor is used as the alloyfor a phosphor precursor, the powder having an angle of repose of 45° orless.

The production method of the present invention may satisfy any two ormore of requirements 1) to 4) as needed. In this case, the amount ofheat generated per certain period of time can be further reduced. Whenrequirement 1) is satisfied, any one of requirements 2) to 4) may besatisfied in addition to requirement 1). Particularly preferably, bothrequirements 1) and 2) or both requirements 1) and 3) are satisfied.Alternatively, both requirements 2) and 3) are preferably satisfied.Preferably, requirements 1) to 4) are appropriately selected because thedegree of effectiveness obtained by requirements 1) to 4) may bedifferent in response to other conditions such as the composition andshape of the alloy for a phosphor precursor, a firing apparatus, afiring atmosphere, and a firing temperature.

To increase the amount of the raw material for the phosphor treated atone time and improve light emission properties of a phosphor to beobtained, requirements 1) to 4) are preferably satisfied. Alternatively,the mass ratio of the mass of the raw material for the phosphor to themass of the firing vessel used in firing the raw material for thephosphor, the mass ratio being represented by the formula [A], may becontrolled to a proper value such that the temperature change per minutein the heating step is 50° C. or lower even if requirements 1) to 4) arenot satisfied. The control of the value of the formula [A] describedbelow in addition to the satisfaction of any one of requirements 1) to4) may result in the control the temperature change per minute in theheating step:

(Mass of raw material for phosphor)/{(mass of firing vessel)+(mass ofraw material for phosphor)}  [A].

The firing vessel has a function to absorb heat liberated by the rawmaterial for the phosphor. Thus, a low ratio of the mass of the rawmaterial for the phosphor to the total of the mass of the firing vesseland the mass of the raw material for the phosphor tends to inhibit theprogress of a rapid exothermic reaction in the heating step.

A preferred value of the formula [A] when the production method of thepresent invention does not satisfy requirements 1) to 4) variesdepending on the composition and shape of the alloy for a phosphorprecursor (in particular, particle diameters of an alloy powder), thetotal content of metal elements in the nitrogen-containing alloy, otherproduction conditions, and the like. In this case, the value of theformula [A] is usually 0.01 or more and preferably 0.05 or more andusually 0.5 or less and preferably 0.2 or less.

In the case where the production method of the present inventionsatisfies at least any one of requirements 1) to 4), a high-performancephosphor can be obtained even when the value of the formula [A] is largecompared with the case where the production method of the presentinvention does not satisfy requirements 1) to 4). A specific range ofvalues are described below.

In the case where the production method of the present inventionsatisfies requirement 1), the value of the formula [A] is usually 0.3 ormore and preferably 0.4 or more, and usually 0.95 or less and preferably0.8 or less from the viewpoint of achieving good properties andproductivity of a phosphor to be obtained.

In the case where the production method of the present inventionsatisfies requirements 1) and 2), the value of the formula [A] isusually 0.35 or more and preferably 0.45 or more, and usually 0.95 orless and preferably 0.8 or less from the viewpoint of achieving goodproperties and productivity of a phosphor to be obtained.

In the case where the production method of the present inventionsatisfies requirements 1) and 3), the value of the formula [A] isusually 0.35 or more and preferably 0.45 or more, and usually 0.6 orless and preferably 0.4 or less from the viewpoint of achieving goodproperties and productivity of a phosphor to be obtained.

In the case where the production method of the present inventionsatisfies requirements 1) and 4), the value of the formula [A] isusually 0.1 or more and preferably 0.2 or more, and usually 0.8 or lessand preferably 0.6 or less from the viewpoint of achieving goodproperties and productivity of a phosphor to be obtained.

To reduce the production cost, the amount of the raw material for thephosphor treated at one time is preferably increased. Thus, in the casewhere the production method of the present invention is industriallyperformed, preferably, the value of the formula [A] is set at 0.24 ormore and preferably 0.4 or more, and the production conditions areadjusted so as to provide a high-performance phosphor.

In the formula [A], the quantity ratio of the raw material for thephosphor to the firing vessel is expressed by mass for convenience. Moreexactly, the value specified by the formula [A] is expressed as theproduct of mass and specific heat (i.e., heat capacity) represented bythe formula [A′]:

Mass of raw material for the phosphor (g)×specific heat of raw materialfor the phosphor/{(mass of firing vessel (g)×specific heat of firingvessel)+(mass of raw material for the phosphor (g)×specific heat of rawmaterial for the phosphor)}  [A′].

For example, the alloy (Eu_(0.008)Sr_(0.792)Ca_(0.2)AlSi) for thephosphor precursor used in Example 1 has a specific heat of 0.71 J/K/g.Boron nitride (constituting the firing vessel) has a specific heat of2.9 J/K/g. Molybdenum has a specific heat of 0.26 J/K/g. Alumina has aspecific heat of 0.6 J/K/g. Aluminum nitride has a specific heat of 1.2J/K/g.

The specific heat of the raw material for the phosphor varies dependingon the composition of the raw material for the phosphor and theincorporation of the nitrogen-containing alloy and a nitride and/oroxynitride described below; hence, a preferred value of the formula [A′]is changed. The value of the formula [A′] is usually 0.05 or more andpreferably 0.1 or more, and usually 0.9 or less and preferably 0.75 orless.

To increase the amount of heat absorbed by the firing vessel, it is thuspreferred to use a firing vessel having a high thermal conductivity or ahigh specific heat. Specifically, a firing vessel composed of boronnitride, molybdenum, alumina, or the like is preferably used. Amongthese, a firing vessel composed of boron nitride is particularlypreferably used.

To further increase the amount of the raw material for the phosphortreated at one time, the amount of heat accumulated in the firingapparatus and the firing vessel should be minimized. The amount of heataccumulated may be adjusted by, for example, adjusting the distancebetween the firing vessels to improve heat dissipation performance,arranging a cooling unit near the firing vessel, using a firing vesselhaving a large surface area, or adjusting the number of firing vesselsplaced in the furnace.

In the case where the production method of the present invention isindustrially performed, the ratio of the volume of the raw material forthe phosphor to the volume of a treatment chamber of the firingapparatus (hereinafter, referred to as a “filling rate of the rawmaterial for the phosphor in the firing vessel”) is important from theviewpoint of achieving good productivity. A specific range of the ratioof the volume of the raw material for the phosphor to the volume of thetreatment chamber of the firing apparatus is usually 8% or more,preferably 20% or more, and more preferably 25% or more, and usually 80%or less, preferably 60% or less, and more preferably 40% or less. In thecase where the filling rate of the raw material for the phosphor in thefiring vessel is lower than the range above, although a phosphor can beeasily produced according to the present invention even when at leastany one of requirements 1) to 4) is not satisfied, the productivitytends to be low. In contrast, in the case where the filling rate of theraw material for the phosphor in the firing vessel is higher than therange above, the degradation of the firing apparatus may be accelerated.

Steps in the production method of the present invention will bedescribed in detail below.

Requirements 1) to 4) will be also described in detail below.

In the production method of the present invention, the phosphor of thepresent invention is produced through steps described below.

That is, raw material metals or alloys thereof are weighed (step ofweighing raw materials). These raw materials are melted (melting step)into an alloy to form the alloy for a phosphor precursor. Then the alloyfor a phosphor precursor is subjected to nitridation by heating under anitrogen-containing atmosphere (heating step; hereinafter, also referredto appropriately as a “secondary nitridation step”). In addition tothese steps, a casting step, a milling step, a classification step, aprimary nitridation step, a cooling step, and the like may be performedas needed.

Any alloy for a phosphor precursor may be used as long as a phosphorhaving a target composition is obtained. One or two or more alloys forthe phosphor precursor may be used.

To satisfy requirement 1), the primary nitridation step should beperformed. Alternatively, the nitrogen-containing alloy described belowshould be incorporated in the secondary nitridation step.

To satisfy requirement 2), the heating rate in the secondary nitridationstep should be controlled.

To satisfy requirement 3), the oxide or oxynitride should be mixed inthe secondary nitridation step.

To satisfy requirement 4), a method including steps (a) to (c) describedbelow (for example, a gas atomization method) is employed in the millingstep, thereby producing a powder of the alloy for a phosphor precursor,the powder having an angle of repose of 45° or less. Alternatively, thesecondary nitridation step should be performed using a powder of thealloy for a phosphor precursor, the powder having an angle of repose of45° or less.

[1] Production of Alloy for a Phosphor Precursor {Weighing of RawMaterial}

In the case where, for example, a phosphor having a compositionrepresented by the general formula [1] described below is produced bythe production method of the present invention, preferably, raw materialmetals or alloys thereof (hereinafter, also referred to simply as “rawmaterial metals”) are weighed in such a manner that a composition of thegeneral formula [3] is achieved, and then the production of the alloyfor a phosphor precursor is performed:

M ¹ _(a) M ² _(b) M ³ _(c) M ⁴ _(d)  [3]

(wherein M¹, M², M³, M⁴, a, b, c, and d are defined the same as in thegeneral formula [1] described below).

Examples of the raw material that can be used include metals and alloysthereof. A raw material corresponding to an element contained in thephosphor of the present invention may be used alone. Alternatively, anytwo or more of such raw materials may be combined in any proportion.Among such raw materials, a Eu raw material or a Ce raw material used asa raw material for the activating element M¹ is preferably metallic Euor metallic Ce because of easy availability thereof.

The purity of metals used to produce the alloy is preferably high.Specifically, from the viewpoint of achieving good light emissionproperties of the phosphor synthesized from the alloy, a raw materialmetal for the activating element M¹ is preferably purified so as to havean impurity content of 0.1% by mole or less and more preferably 0.01% bymole or less. Raw materials containing elements other than theactivating element M¹ are various metals such as divalent metals,trivalent metals, and tetravalent metals. From the same reason as theactivating element M¹, each of the raw materials preferably has animpurity content of 0.1% by mole or less and more preferably 0.01% bymole or less. For example, in the case where at least one elementselected from the group consisting of Fe, Ni, and Co is contained as animpurity element, the content of each element is usually 500 ppm or lessand preferably 100 ppm or less.

The shape of raw material metals is not limited. The raw material metalsare usually in the form of particles or blocks each having a diameter ofseveral millimeters to several tens of millimeters. The raw materialmetals each having a diameter of 10 mm or more is referred to as the“blocks” defined here. The raw material metals each having a diameter ofless than 10 mm is referred to as the “particles” defined here.

In the case where an alkaline-earth metal is used as the divalent metalelement M², examples of the shape of the raw material thereof include,but are not limited to, particles and blocks. It is preferable to choosean appropriate shape considering the chemical characteristics of the rawmaterials. For example, Ca may be used in both forms of particles andblocks because of its proven stability in air, whereas Sr is preferablyused in the form of blocks since it has higher chemical activity thanCa.

With respect to metal elements in which the amounts of the metalelements are reduced by, for example, evaporation or reactions with amaterial constituting a crucible while the metal elements are beingmelted, excessive amounts of the metal elements may be weighed inadvance as needed.

{Melting of Raw Material}

After the raw materials are weighed, the raw materials are melted intoan alloy to form an alloy for a phosphor precursor (melting step). Theresulting alloy for a phosphor precursor contains two or more metalelements constituting a phosphor prepared in the present invention(hereinafter, also referred to as a “phosphor of the presentinvention”). A single alloy for a phosphor precursor need not containall metal elements constituting the phosphor of the present invention.Two or more alloys and/or metals may be further incorporated in theprimary nitridation step or secondary nitridation step to produce thephosphor of the present invention.

A method for melting the raw material metals is not particularlylimited. Any method may be employed. Examples of such a method that canbe employed include resistance heating, electron beam melting, arcmelting, and high-frequency induction heating (hereinafter, alsoreferred to as “high-frequency melting”). Furthermore, any two or moreof these methods may be combined for melting.

Examples of a material for a crucible that can be used during themelting include alumina, calcia, graphite, and molybdenum.

However, in particular, when an alloy, containing Si and analkaline-earth metal element serving as the divalent metal element M²,for the phosphor precursor is produced, the following points should bepreferably noted.

That is, the melting point of Si is 1,410° C. and comparable to theboiling points of alkaline earth metals (e.g., Ca has a boiling point of1,494° C., Sr has a boiling point of 1,350° C., and Ba has a boilingpoint of 1,537° C.). In particular, the boiling point of Sr is lowerthan the melting point of Si, and this makes it extremely difficult tomelt Sr and Si simultaneously.

Accordingly, in the present invention, preferably, a raw materialcontaining Si (i.e., Si and/or an alloy containing Si) is first melted,and then a raw material for an alkaline-earth metal (i.e., analkaline-earth metal and/or an alloy containing an alkaline-earth metal)is melted. In this way, it is possible to melt the raw material for analkaline-earth metal together with the raw material for Si. Furthermore,by melting the raw material for Si and then melting the raw material foran alkaline-earth metal, the resulting alloy for a phosphor precursorhas a higher purity, so that the resulting phosphor prepared from thealloy has significantly improved properties.

Production of such an alloy, containing Si and an alkaline-earth metalelement, for the phosphor precursor will be described in detail below.

In the case of the production of the alloy, containing Si and analkaline-earth metal element, for the phosphor precursor, a meltingmethod is not limited. Any of these melting methods described above maybe employed. Among these methods, arc melting and high-frequency meltingare preferred, and high-frequency melting is particularly preferred.Hereinafter, (1) arc melting or electron beam melting and (2)high-frequency melting will be taken as examples for detailedexplanation.

(1) Arc Melting or Electron Beam Melting

In arc melting or electron beam melting, raw material metals are meltedin the following steps.

i) Metal Si or an alloy containing Si is melted with electron beams orarc discharge.

ii) Then, an alkaline-earth metal is melted by indirect heating to forman alloy containing both Si and the alkaline earth metal.

This method may be performed by first adding the molten alkaline-earthmetal to the molten metal containing Si and then heating and/or stirringthe mixture with electron beams or arc discharge to promote the mixingthereof.

(2) High-Frequency Melting

An alloy containing an alkaline-earth metal element is highly reactivewith oxygen and thus should be melted not in air but in vacuum or aninert gas. Under such conditions, high-frequency melting is generallypreferable. However, Si is a semiconductor and difficult to melt byinduction heating with a high frequency. For example, at 20° C., thespecific resistance of aluminum is 2.8×10⁻⁸ Ω·m, while that ofpolycrystalline Si for semiconductors is 10⁵ Ω·m or higher. Substanceswith a high specific resistance, such as Si, cannot be easily melteddirectly by high-frequency dielectric heating, and thus they are usuallymelted with the help of an electrically conductive susceptor, whichtransfers heat to Si via thermal conduction or thermal radiation.

The shape of the susceptor is not limited. Although a disk-shapedsusceptor or a cylindrical susceptor may be used, a crucible ispreferably used as such a susceptor.

A material for the susceptor is not limited as long as the raw materialcan be melted. Typical examples of the material for the susceptorinclude graphite, molybdenum, and silicon carbide. Disadvantageously,these materials are very expensive and highly reactive withalkaline-earth metals. However, a crucible in which alkaline-earthmetals can be melted (e.g., alumina or calcia) is composed of aninsulating material and thus difficult to use as a susceptor. It istherefore difficult to simultaneously melt an alkaline-earth metal andmetal Si placed in a known electrically conductive crucible (composedof, for example, graphite), serving as a susceptor, by indirect heatingbased on high-frequency melting. This problem can be solved by thefollowing steps.

i) Metal Si is melted in an electrically conductive crucible by indirectheating.

ii) Then, an alkaline-earth metal is melted in an insulating crucible toform an alloy containing both Si and the alkaline-earth metal.

The metal Si may be cooled between the steps i) and ii) or directlyforwarded to the step of melting the alkaline-earth metal without beingcooled. If the steps i) and ii) are consecutively performed, a crucibleproduced by coating an electrically conductive vessel with, for example,calcia or alumina that is suitable for melting of alkaline-earth metalsmay be used.

These steps can be described in more detail as follows.

i) Metal Si and another metal M (e.g., Al or Ga) are melted in anelectrically conductive crucible by indirect heating to form anelectrically conductive alloy (a mother alloy).

ii) Then, another crucible that is resistant to alkaline earth metals isused to melt the mother alloy prepared in the step i), and subsequentlyan alkaline-earth metal is melted with a high frequency to form an alloycontaining Si and the alkaline-earth metal element.

An example of a specific method in which metal Si or a mother alloycontaining Si is first melted and then an alkaline-earth metal is meltedis a method in which metal Si or a mother alloy containing Si is firstmelted and then an alkaline-earth metal is added thereto.

In addition, Si may be alloyed with a metal M other than the divalentmetal element M² so as to have electrical conductivity. In this case,the melting point of the resulting alloy is preferably lower than thatof Si. The alloy of Si and Al is particularly preferable because themelting point thereof is approximately 1,010° C. and thus is lower thanthe boiling points of alkaline earth metal elements.

In the case where a mother alloy of Si and a metal M other than thedivalent metal element M² is used, the composition thereof is notparticularly limited, but the mother alloy preferably has electricconductivity. In this case, preferably, the mixing ratio (molar ratio)of the metal M is usually in the range of 0.01 to 5 with respect to thenumber of moles of Si being one, so that the resulting mother alloy hasa melting point lower than the boiling points of alkaline-earth metalelements. Moreover, metal Si may be further added to the mother alloycontaining Si.

In the present invention, metal Si should be melted before analkaline-earth metal is melted, but the timing to melt raw materialmetals other than the metal Si and the alkaline-earth metal is notparticularly limited. Usually, the raw material metal that is abundantlyused or has a high melting point is preferentially melted.

To uniformly disperse the activating element M¹, metal Si is preferablymelted before the raw material metal for the activating element M¹ ismelted because of a small amount of the activating element M¹ added.

To produce an alloy for a phosphor precursor that is represented by thegeneral formula [3] and contains Si as the tetravalent metal element M⁴and at least Sr as the divalent metal element M², the following meltingsteps are preferably used.

(1) A mother alloy of Si and the trivalent metal element M³ is prepared.In this step, Si and the trivalent metal element M³ are preferablyalloyed in accordance with a ratio of Si to M³ in the general formula[3].

(2) The mother alloy prepared in the step (1) is melted and then Sr ismelted.

(3) Then a divalent metal element other than Sr and the activatingelement M¹ are melted.

Also in the case where any raw material is melted, specific temperatureconditions and a period of time for melting of the raw material may beappropriately set in response to the raw material used.

Any atmosphere under which the raw material is melted may be used aslong as an alloy for a phosphor precursor is prepared. The atmosphere ispreferably an inert gas, in particular, argon. A single inert gas may beused. Alternatively, any two or more inert gases may be combined in anyproportion.

Any pressure at which the raw material is melted is used as long as analloy for a phosphor precursor is prepared. The pressure is preferablyin the range of 1×10³ Pa to 1×10⁵ Pa. In view of safety, the rawmaterial is desirably melted at atmospheric pressure or less.

{Casting of Molten Metal}

The raw material is melted to prepare an alloy for a phosphor precursor.Although the alloy for a phosphor precursor is usually obtained as amolten alloy, there are many technical difficulties in directlyproducing a phosphor from the molten alloy. Thus, the molten alloy ispreferably subjected to a casting step of pouring the molten alloy intoa mold, thereby preparing a solidified alloy (hereinafter, also referredto as an “alloy ingot”).

In this casting step, however, segregation may occur depending on therate of cooling the molten alloy. In other words, the molten alloyhaving a uniform composition is cooled into the solid alloy having anonuniform composition distribution, in some cases. Thus, the coolingrate is preferably maximized. Preferably, the mold is composed of amaterial such as copper having a high thermal conductivity and has ashape that promotes heat dissipation. Furthermore, the mold ispreferably cooled by a technique such as water cooling, as needed.

Preferably, the molten alloy is poured into, for example, a mold havinga large bottom area relative to its thickness in order to solidify themolten alloy as rapidly as possible.

Additionally, the degree of segregation varies depending on thecomposition of the alloy. It is thus preferable to analyze the samplesobtained from several points of the alloy ingot with regard to theircomposition by a necessary analytical technique such as ICP emissionspectrometry in order to determine the cooling rate required for theprevention of the segregation.

An inert gas atmosphere is preferred during the casting. An argonatmosphere is particularly preferred. The inert gas may be used alone. Asingle inert gas may be used. Alternatively, any two or more inert gasesmay be combined in any proportion.

{Milling of Alloy Ingot}

Before the heating step, the alloy for a phosphor precursor ispreferably formed into a powder having desired particle diameters. Thealloy ingot prepared in the casting step is preferably milled (millingstep) into the alloy powder, having desired particle diameters andparticle size distribution, for the phosphor precursor (hereinafter,also referred to simply as an “alloy powder”).

Examples of a milling method that can be employed include, but are notparticularly limited to, dry milling and wet milling which uses anorganic solvent such as ethylene glycol, hexane, or acetone.

This milling step will be described in detail below taking dry millingas an example. This milling step may be divided into several substepsincluding coarse milling, medium milling, and fine milling substeps, asneeded. In this case, the same apparatus may be used in all thesubsteps. Alternatively, different apparatuses may be used in thesubsteps.

The coarse milling substep herein means a substep of milling the alloypowder in such a manner that about 90% by weight of the alloy particleshave diameters of 1 cm or less. Examples of a mill that can be used inthis substep include a jaw crusher, a gyratory crusher, a crushing roll,and an impact crusher. The medium milling substep means a substep ofmilling the alloy powder in such a manner that about 90% by weight ofthe alloy particles have diameters of 1 mm or less. Examples of a millthat can be used in this substep include a cone crusher, a crushingroll, a hammer mill, and a disk mill. The fine milling substep means asubstep of milling the alloy powder in such a manner that the alloyparticles have a weight-average median diameter described below.Examples of a mill that can be used in this substep include a ball mill,a tube mill, a rod mill, a roller mill, a stamp mill, an edge-runner, avibrating mill, and a jet mill.

Particularly in the final milling substep, a jet mill is preferably usedwith the intention of preventing the incorporation of impurities. Thealloy ingot is preferably ground in advance into particles withdiameters of about 2 mm or less for the use of a jet mill. Such a jetmill injects a fluid from its nozzle into the atmospheric pressure so asto grind particles with the expansion energy generated in associationwith the injection, thereby enabling the control of the particlediameter by changing the milling pressure and the prevention of impurityincorporation. The gauge pressure of milling varies depending on thetype of apparatus used but is usually in the range of 0.01 MPa to 2 MPa,preferably from 0.05 MPa and less than 0.4 MPa, and more preferably inthe range of 0.1 MPa to 0.3 MPa. An excessively low gauge pressure islikely to lead to excessively large particle diameters of the resultingparticles. An excessively high gauge pressure is likely to lead toexcessively small particle diameters of the resulting particles.

To prevent the contamination of the alloy with impurities such as ironin any milling substep, the compatibility between a materialconstituting a mill and the alloy to be ground always has to be good.For example, surfaces to be in contact with particles are preferablylined with ceramic, in particular, alumina, silicon nitride, tungstencarbide, zirconia, or the like.

Furthermore, to prevent the oxidation of the alloy powder, the millingstep is preferably performed under an inert gas atmosphere. The type ofinert gas is not particularly limited. Usually, gases, such as nitrogen,argon, and helium, may be used alone or in combination of two or morethereof. Considering the cost, nitrogen is particularly preferable.

The oxygen concentration in the atmosphere is not limited as long as theoxidation of the alloy powder is prevented. The oxygen concentration isusually 10% by volume or less and particularly preferably 5% by volumeor less. The lower limit of the oxygen concentration is usually about 10ppm. The oxygen concentration controlled to fall within such a specificrange probably contributes to the formation of oxide layers on the alloypowder during the milling step and thereby stabilizes the particles.Performing the milling step in an atmosphere containing more than 5% byvolume of oxygen would involve the risk of dust explosion and thuspreferably require equipment for suppressing the generation of dust.

The alloy powder may be cooled in the milling step in such a manner thatthe temperature of the alloy powder is prevented from being increased.

{Classification of Alloy Powder}

Preferably, the resulting alloy powder is screened (classification step)with a screening apparatus based on meshes, such as a vibrating screenand a sifter, an inertial classification apparatus such as an airseparator, or a centrifuge such as a cyclone separator so as to have adesired value of the weight-average median diameter D₅₀ and desiredparticle size distribution, and then the resulting alloy powder issubjected to the subsequent steps.

In controlling the particle size distribution, it is preferable toclassify coarse particles and return the classified particles to a mill,and it is more preferably to repeat this cycle of classification and/orreturn seamlessly.

Preferably, the classification step is also performed under an inert gasatmosphere. The type of inert gas is not particularly limited. Usually,inert gases, such as nitrogen, argon, and helium, may be used alone orin combination of two or more thereof. From the viewpoint of achievinggood economy, nitrogen is particularly preferable. The oxygenconcentration in the inert gas atmosphere is preferably 10% by volume orless and particularly preferably 5% by volume or less.

The diameters of the alloy powder used in the primary nitridation stepand the secondary nitridation step described below should be controlledin response to the activities of metal elements constituting the alloypowder. The weight-average median diameter D₅₀ is usually 100 μm orless, preferably 80 μm or less, and particularly preferably 60 μm orless, and 0.1 μm or more, preferably 0.5 μm or more, and particularlypreferably 1 μm or more. In the case where the alloy contains Sr, thealloy is highly reactive with a surrounding gas. Thus, theweight-average median diameter D₅₀ of the alloy powder is usually 5 μmor more, preferably 8 μm or more, more preferably 10 μm or more, andparticularly preferably 13 μm or more. When the alloy powder hasparticle diameters smaller than the range of the weight-average mediandiameter D₅₀ described above, heating rates in nitridation and otherreactions tend to increase. This makes it difficult to control suchreactions, in some cases. In addition, the alloy powder is easilyoxidized in air; hence, for example, oxygen is easily incorporated intoa phosphor to be obtained. Thus, such alloy powder is difficult tohandle, in some cases. On the other hand, when the alloy powder hasparticle diameters larger than the range of the weight-average mediandiameter D₅₀ described above, reactions such as nitridation proceedinsufficiently inside each alloy particle, in some cases.

The proportion of alloy particles having a size of 10 μm or less in thealloy powder is preferably 80% by weight or less. The proportion ofalloy particles having a size of 45 μm or more is preferably 40% byweight or less.

The value of QD is not particularly limited but is usually 0.59 or less.QD is defined by the expression: QD=(D₇₅−D₂₅)/(D₇₅+D₂₅) where D₂₅represents a particle size corresponding to an integrated value of 25%,and D₇₅ represents a particle size corresponding to an integrated valueof 75%. A low value of QD means a narrow particle size distribution.

[II] Heating Step

In the present invention, the resulting alloy for a phosphor precursor(the alloy for a phosphor precursor may be in the form of a powder orblocks but is preferably the alloy powder for the phosphor precursordescribed above) and/or the nitrogen-containing alloy described beloware subjected to nitridation by heating in a nitrogen-containingatmosphere. In the heating step, the secondary nitridation stepdescribed below is absolutely necessary. The primary nitridation stepdescribed below is performed as needed.

{Primary Nitridation Step}

In the case where the phosphor of the present invention is produced bythe production method satisfying requirement 1) in order to industriallyefficiently produce the phosphor of the present invention, the primarynitridation step is performed before the secondary nitridation step, asneeded. The primary nitridation step is a step of subjecting the alloypowder (may also be in the form of particles or blocks) to nitridationto produce the nitrogen-containing alloy described below. Specifically,the primary nitridation step is a preliminary nitridation step ofheating the alloy powder under a nitrogen-containing atmosphere in apredetermined temperature range for a predetermined period of time.Employment of the primary nitridation step results in control of thereactivity between the alloy and nitrogen in the secondary nitridationstep, thereby making it possible to industrially produce a phosphor fromthe alloy.

The alloy powder is subjected to nitridation in this step. As a result,the material constituting the alloy powder is converted from the alloyfor a phosphor precursor into a nitrogen-containing alloy, therebyincreasing the weight thereof. In this specification, the increase inthe weight of the alloy powder is expressed as the rate of weightincrease represented by the formula [4]:

(Weight of nitrogen-containing alloy after primary nitridationstep−weight of alloy powder before primary nitridation step)/weight ofalloy powder before primary nitridation step×100  [4].

In this step, the degree of nitridation can be controlled by reactionconditions such as the nitrogen partial pressure, the temperature, andthe heating time.

While the rate of weight increase also depends on the reactionconditions in the secondary nitridation step, the composition of thealloy powder, and the like, the reaction conditions are preferablyadjusted in such a manner that the rate of weight increase determined bythe formula [4] is usually 0.5% by weight or more, preferably 1% byweight or more, particularly preferably 5% by weight or more. The upperlimit of the rate of weight increase is not particularly limited but is,in theory, usually 40% by weight or less and preferably 31% by weight orless. To adjust the rate of weight increase of the alloy powder withinthe range above, the primary nitridation step may be repeated twice ormore. In the case of repeating the primary nitridation step, the numberof repetitions is not particularly limited but is usually three times orless and preferably twice or less, in view of the production cost.

The primary nitridation step may be performed by a continuous process orbatch process. Preferred reaction conditions differ between thecontinuous process and the batch process. Thus, with regard to thereaction conditions in the primary nitridation step, the continuousprocess and the batch process will be separately described below.

From the viewpoint of achieving good productivity, the continuousprocess is more preferable than the batch process. That is, in the casewhere the primary nitridation step is performed by the continuousprocess, heating is preferably performed at a higher concentration ofnitrogen and a higher temperature for a shorter period of time comparedwith those in the batch process.

<Continuous Process> Type of Apparatus

In the case where the primary nitridation step is performed by thecontinuous process, an apparatus, e.g., a rotary kiln, a tunnel furnace,a belt furnace, or a fluidized-bed furnace, may be used. In particular,a rotary kiln is preferably used.

In the case of using the rotary kiln, an alloy powder is heated under astream of a nitrogen-containing gas while a refractory cylindricalfurnace tube is being rotated. Continuous feeding of the alloy powderinto the inclined furnace tube makes it possible to perform continuoustreatment. The use of the rotary kiln makes it possible to stir thealloy powder during the heating, thereby inhibiting the fusion ofparticles of the alloy powder and thus improving the gas-solid contactefficiency. This results in uniform nitridation treatment and areduction in heating time. The rotary kiln preferably has a structurethrough which an atmospheric gas can pass. Furthermore, the rotary kilnis preferably capable of controlling the residence time and the feedrate of an alloy powder.

Alternatively, an alloy powder may be subjected to nitridation with avertical furnace while the alloy powder is being dropped therein.

Any rotation speed of the furnace tube may be used as long as anitrogen-containing alloy is obtained. The rotation speed is usually 1rpm or more, preferably 2 rpm or more, and particularly preferably 3 rpmor more, and usually 100 rpm or less, preferably 20 rpm or less, andparticularly preferably 8 rpm or less. A rotation speed outside thisrange may make it difficult to control the motion of the alloy powder.That is, an excessively slow rotation speed is liable to cause adhesionand residence of the alloy powder to the inner wall of the furnace tube.On the other hand, an excessively high rotation speed is liable to causea reduction in mixing efficiency because the alloy powder is forcedagainst the inner wall of the furnace tube by centrifugal force and isnot dropped.

Any angle of inclination of the furnace tube with respect to thehorizontal direction is used as long as a nitrogen-containing alloy isobtained. The angle of inclination is usually 0.6° or more, preferably1° or more, particularly preferably 1.7° or more, and usually 6° orless, preferably 5° or less, and particularly preferably 3.4° or less.An angle of inclination outside the range above tends to make itdifficult to control the feed rate of the alloy powder.

In the case where the primary nitridation step is performed with therotary kiln, it is preferable to prevent adhesion of the alloy powder tothe furnace tube. Adhesion of the alloy powder may preclude thedischarge of the treated powder and make it difficult to stably performthe treatment. Furthermore, in the case where the furnace tube is heatedfrom the outside with, for example, a heater, adhesion of the alloypowder may substantially reduce the heating temperature due to theeffect of the adherend serving as a heat insulator. After the completionof the primary nitridation step, the adherend is detached and removed onaccount of, for example, the difference in thermal expansion coefficientbetween the furnace tube and the alloy powder in cooling the furnacetube, in some case. To maintain a constant level of the discharge rateof the nitrogen-containing alloy and a constant degree of nitridation inthe primary nitridation step, however, it is more preferable to continueto remove the adherend by, for example, applying vibration and the liketo the furnace tube to detach the adherend or physically scraping theadherend away.

Material of Apparatus

In an apparatus used in the continuous process, any materialconstituting components, such as a firing vessel and a furnace tube, tobe in contact with an alloy powder may be used as long as anitrogen-containing alloy is obtained. Examples of the material that canbe used include aluminum oxide, boron nitride, graphite, calcium oxide,magnesium oxide, molybdenum, and tungsten. In the case where theapparatus is used at about 1,100° C. or lower, quartz may also be used.Among these, aluminum oxide and boron nitride are particularlypreferably used for the furnace tube. These materials may be used aloneor in any combination of two or more in any proportion.

Atmosphere During Heating

An atmosphere during heating essentially contains a nitrogen element. Amixed gas of nitrogen gas and an inert gas other than nitrogen gas flowspreferably. In particular, a mixed gas of nitrogen and a rare gaselement such as argon flows preferably. This is because theincorporation of such an inert gas into nitrogen gas makes it possibleto control the rate of reaction. The inert gases described above may beused alone or in any combination of two or more in any proportion.

The nitrogen concentration in the atmosphere is not limited as long as anitrogen-containing alloy is obtained. The nitrogen concentration isusually 0.1% by volume or more, preferably 1% by volume or more, andmore preferably 3% by volume or more. The upper limit is notparticularly limited but is preferably 80% by volume or less. Anexcessively low nitrogen concentration may lead to the insufficientprogress of nitridation. On the other hand, an excessively high nitrogenconcentration may make it difficult to control the heating temperatureand may increase the amount of the alloy adhering to the furnace tubeand the like.

Any oxygen concentration in the atmosphere may be used as long as anitrogen-containing alloy is obtained. The oxygen concentration isusually 300 ppm or less and preferably 100 ppm or less, and preferablyalmost zero, usually 0.1 ppm or more, and preferably 1 ppm or more. Anexcessively high oxygen concentration in the atmosphere may cause theincorporation of oxygen into a nitrogen-containing alloy and a finalphosphor, thereby reducing the peak emission wavelength and brightness.

To prevent the incorporation of oxygen, a reducing gas (e.g., hydrogen,carbon monoxide, hydrocarbon, or ammonia) is preferably incorporatedinto the atmosphere in an amount such that the concentration of thereducing gas is below the explosive limit. The reducing gas may be usedalone. Alternatively, two or more reducing gases may be combined in anyproportion.

Any pressure may be used during heating as long as a nitrogen-containingalloy is obtained. To prevent the contamination of the system withoxygen in air, the pressure is preferably equal to or higher than theatmospheric pressure. If a furnace used is less airtight, an excessivelylow pressure may cause the contamination of the system with a largeamount of oxygen and a deterioration in the performance of a phosphorproduced.

Any nitrogen partial pressure in the atmosphere may be used duringheating as long as a nitrogen-containing alloy is obtained. The nitrogenpartial pressure is usually equal to or lower than the atmosphericpressure, preferably 0.09 MPa or less, and more preferably 0.08 MPa orless, and usually 0.0005 MPa or more and preferably 0.001 MPa or more. Ahigher nitrogen partial pressure results in a higher rate ofnitridation. An excessively high nitrogen partial pressure results in anexcessively high heat generation rate, so that the temperature of thealloy powder may exceed the melting point of the alloy constituting thealloy powder to fuse the alloy particles. This may cause nonuniformnitridation. On the other hand, an excessively low nitrogen partialpressure may cause industrial problems of, for example, a prolongedperiod of time required for the primary nitridation step and an increasein the amount of the atmospheric gas consumed (e.g., argon gas).Furthermore, Sr or the like may be evaporated from the alloy to causethe deviation of the composition.

Amount of Nitrogen Fed and Feed Rate

In the case of the continuous process, preferably, a predeterminedamount of the alloy powder per unit time is fed into the apparatus. Tosubject the fed alloy powder to nitridation to a desired extent, atleast the amount of nitrogen theoretically required per unit time is fedinto the apparatus. Specifically, a nitrogen-containing atmospheric gasis preferably fed into the apparatus, the nitrogen content being usually5% by weight or more and preferably 10% by weight or more, and (theupper limit is not particularly limited) usually 200% by weight or lesswith respect to the weight of the alloy powder fed per unit time.

The nitrogen-containing atmospheric gas may flow in the countercurrentdirection or parallel-flow direction with respect to the feed directionof the alloy powder. Usually, the nitrogen-containing atmospheric gasflows in the countercurrent direction.

Heating Conditions

Any heating temperature may be used as long as a nitrogen-containingalloy is obtained. The heating temperature is usually equal to or higherthan a temperature 150° C. lower than the melting point of the alloy fora phosphor precursor and preferably equal to or higher than atemperature 100° C. lower than the melting point of the alloy for thephosphor precursor, and usually equal to or lower than a temperature 10°C. lower than the melting point of the alloy for the phosphor precursor.More specifically, while the heating temperature varies depending on thecomposition of the alloy, the heating temperature is, for example,usually 800° C. or higher and preferably 900° C. or higher, and usually2,500° C. or lower and preferably 1,500° C. or lower. An excessively lowheating temperature is liable to lead to the insufficient progress of anitridation reaction. On the other hand, an excessively high heatingtemperature is liable to cause an increase in the amount of the alloypowder adhering to the furnace tube.

The heating temperature defined here represents the temperature of thefurnace tube during heating.

The temperature 100° C. lower than the melting point of the alloy forthe phosphor precursor means an approximate temperature of initiation ofthe nitridation of the alloy for the phosphor precursor.

In this specification, the melting points of the alloys such as thealloy for a phosphor precursor and the nitrogen-containing alloy can bedetermined from endothermic peaks measured bythermogravimetry-differential thermal analysis (hereinafter,appropriately referred to as “TG-DTA”) as described in examples below.The melting points vary depending on the compositions of the alloys. Themelting points are about 900° C. to about 1,300° C. In the case of analloy exhibiting no clear melting point, the decomposition onsettemperature is regarded as the melting point of the alloy. In the caseof using a plurality of alloys, the melting point of an alloy having thelowest melting point among the alloys is defined as the melting point ofthe alloys.

Any heating time (holding time at the maximum temperature) within thetemperature range above may be used as long as a nitrogen-containingalloy is obtained. The heating time is usually 0.1 minutes or more andpreferably 1 minute or more, and usually 1 hour or less, preferably 30minutes or less, and more preferably 8 minutes or less. An excessivelylong heating time may cause the deviation of the composition due to theevaporation of an alkaline-earth metal. An excessively short heatingtime may lead to the insufficient progress of nitridation.

<Batch Process> Type of Apparatus

In the case where the primary nitridation step is performed by the batchprocess, for example, a tubular furnace, a general atmosphere furnace,and a rotary kiln may be used. As specific operations, usually, an alloypowder is placed into a refractory firing vessel (e.g., tray orcrucible) and heated in such an apparatus.

Firing Vessel

Any shape of the firing vessel into which the alloy powder is placed maybe used as long as a nitrogen-containing alloy is obtained. To increasethe contact efficiency between an atmosphere and the alloy powder duringfiring, preferably, the firing vessel does not have an enclosedstructure, and a packed bed is not excessively high. The height of thepacked bed is usually 30 mm or less, preferably 20 mm or less, and morepreferably 15 mm or less, and usually 3 mm or more and preferably 5 mmor more. An excessively high packed bed may cause a nonuniformnitridation reaction. On the other hand, an excessively low packed bedmay cause a reduction in productivity.

Any material constituting components, such as the firing vessel, to bein contact with an alloy powder may be used as long as anitrogen-containing alloy is obtained. Examples of the material that canbe used include aluminum oxide, boron nitride, graphite, calcium oxide,magnesium oxide, molybdenum, and tungsten. In the case where theapparatus is used at about 1,100° C. or lower, quartz may also be used.Among these, graphite, aluminum oxide, boron nitride, and quartz arepreferably used. More preferably, boron nitride is used. These materialsmay be used alone or in any combination of two or more in anyproportion.

Atmosphere During Heating

An atmosphere during heating is preferably a mixed atmosphere of anitrogen atmosphere and an inert gas atmosphere. In particular, a mixedatmosphere of nitrogen and a rare gas element such as argon ispreferred. This is because the incorporation of the inert gas atmosphereinto the nitrogen gas atmosphere makes it possible to control the rateof reaction. The inert gases described above may be used alone or in anycombination of two or more in any proportion.

The nitrogen concentration in the atmosphere is not limited as long as anitrogen-containing alloy is obtained. The nitrogen concentration isusually 0.1% by volume or more, preferably 1% by volume or more, andmore preferably 3% by volume or more, and usually 99% by volume or less,preferably 20% by volume or less, and more preferably 10% by volume orless. An excessively low nitrogen concentration may lead to theevaporation of an alkali-earth metal or the like. On the other hand, anexcessively high nitrogen concentration may cause the nonuniformprogress of nitridation.

Any oxygen concentration in the atmosphere may be used as long as anitrogen-containing alloy is obtained. The oxygen concentration isusually the same as in the continuous process.

Furthermore, a reducing gas (e.g., hydrogen, carbon monoxide,hydrocarbon, or ammonia) is preferably incorporated into the atmospherein an amount such that the concentration of the reducing gas is belowthe explosive limit, in the same way as in the continuous process.

Any pressure may be used during heating as long as a nitrogen-containingalloy is obtained. To prevent the contamination of the system withoxygen contained in air, the pressure is preferably equal to or higherthan the atmospheric pressure in the same way as in the continuousprocess.

Any nitrogen partial pressure in the atmosphere may be used duringheating as long as a nitrogen-containing alloy is obtained. The nitrogenpartial pressure is usually the same as in the continuous process.

Heating Conditions

Any heating temperature may be used as long as a nitrogen-containingalloy is obtained. The heating temperature is usually equal to or higherthan a temperature 150° C. lower than the melting point of the alloy fora phosphor precursor and preferably equal to or higher than atemperature 100° C. lower than the melting point of the alloy for thephosphor precursor, and usually equal to or lower than the melting pointof the alloy for the phosphor precursor, preferably equal to or lowerthan a temperature 10° C. lower than the melting point of the alloy forthe phosphor precursor, and more preferably equal to or lower than atemperature 50° C. lower than the melting point of the alloy for thephosphor precursor. More specifically, while the heating temperaturevaries depending on the composition of the alloy, the heatingtemperature is, for example, usually 800° C. or higher and preferably900° C. or higher, and usually 2,500° C. or lower and preferably 1,500°C. or lower. An excessively low heating temperature tends to require aprolonged period of time needed for the completion of the primarynitridation step and in some cases, causes the incomplete progress ofnitridation. On the other hand, an excessively high heating temperaturemay make it difficult to control a nitridation reaction in the primarynitridation step to cause the nonuniform progress of nitridation.Furthermore, heating at a temperature close to the melting point of thealloy for the phosphor precursor is liable to cause a reduction inalloy-nitrogen contact efficiency due to the adhesion of the alloypowder to the vessel and the fusion of particles of the alloy. Theheating temperature defined here represents a temperature in the furnaceduring the heating.

The melting point of the alloy is the same as that in the descriptionfor the continuous process.

The heating time varies depending on other conditions such as the typeof apparatus and the heating temperature.

The heating time tends to require a prolonged period of time comparedwith that in the continuous process. The heating time is usually 10minutes or more, preferably 20 minutes or more, and usually 48 hours orless. An excessively long heating time may cause the deviation of thecomposition due to the evaporation of an alkaline-earth metal. Anexcessively short heating time may lead to the insufficient progress ofnitridation. The heating time defined here represents the holding timeat the maximum temperature.

In the temperature range from a temperature 150° C. lower than themelting point of the alloy for the phosphor precursor to a temperature10° C. lower than the melting point of the alloy for the phosphorprecursor, the temperature is preferably increased at a low heatingrate. The heating rate in this temperature range is usually 9° C./min orless and preferably 7° C./min or less. The lower limit of the heatingrate is not particularly limited. From the viewpoint of achieving goodproductivity, the lower limit is usually 0.1° C./min or more andpreferably 0.5° C./min or more.

The heating conditions are not particularly limited in the temperaturerange from a temperature at the initiation of heating to a temperature150° C. lower than the melting point of the alloy for the phosphorprecursor. The temperature may be increased rapidly or slowly. In somecases, in view of the responsiveness of the temperature control of thefiring apparatus, the heating rate may be reduced to 9° C./min or lessfrom a temperature below a temperature 150° C. lower than the meltingpoint of the alloy for the phosphor precursor.

Nitrogen-Containing Alloy

In this specification, the nitrogen-containing alloy represents theforegoing alloy after the completion of the primary nitridation step.

The nitrogen-containing alloy contains two or more metal elementsconstituting a phosphor of the present invention. Furthermore, thenitrogen-containing alloy mainly contains nitrogen as a component otherthan the metal elements. As one of the indices of the degree ofnitridation, the total content of metal elements (percent by weight)determined by the formula [5] can be used. A lower total content ofmetal elements represents a higher degree of nitridation.

The total content of metal elements (wt %)=100−{(weight ofnitrogen-containing alloy after primary nitridation step−weight of alloybefore primary nitridation step)/weight of nitrogen-containing alloyafter primary nitridation step}×100  [5]

The total content (percent by weight) of metal elements in thenitrogen-containing alloy means the content of all metal elements in thenitrogen-containing alloy. A specific range thereof is not limited aslong as a phosphor of the present invention is obtained. The totalcontent of metal elements is usually 60% by weight or more, preferably70% by weight or more, and more preferably 76% by weight or more, andusually 97% by weight or less, preferably 95% by weight or less, andmore preferably 93% by weight or less. At a total content of metalelements exceeding the range above, the effect of the primarynitridation step is not provided, in some cases. In theory, it isunlikely that the total content of metal elements is lower than therange above.

The degree of nitridation of the nitrogen-containing alloy may also bespecified by the nitrogen content (percent by weight). The nitrogencontent can be determined by measuring the amount of nitrogen with, forexample, an oxygen-nitrogen analyzer (manufactured by Leco Corporation)and calculating the nitrogen content from the formula [6]:

Nitrogen content of nitrogen-containing alloy (wt %)=(amount ofnitrogen/weight of nitrogen-containing alloy)×100  [6].

A specific range of the nitrogen content determined using the formula[6] is not limited as long as a phosphor of the present invention isobtained. The nitrogen content is usually 1% by weight or more,preferably 2% by weight or more, and more preferably 5% by weight ormore, and usually 31% by weight or less and preferably 25% by weight orless. An excessively low nitrogen content may cause the insufficientinhibition of heat generation in the secondary nitridation stepdescribed below. An excessively high nitrogen content may beuneconomical in time and energy.

The use of a nitrogen-containing alloy having a nitrogen content, whichis determined by the formula [6], of 10% by weight or more andpreferably 12% by weight or more as a raw material for a phosphorresults in a high effect of inhibiting heat generation in the secondarynitridation step. In this case, regardless of the value of the formula[A], a high-performance phosphor tends to be produced, which isparticularly preferred.

Preferably, the nitrogen-containing alloy satisfies the formula [7]:

0.03≦NI/NP≦0.9  [7]

wherein in the formula [7],

NI represents the nitrogen content (% by weight) of thenitrogen-containing alloy; and

NP represents the nitrogen content (% by weight) of a phosphor to beproduced.

The formula [7] indicates the degree of nitridation of thenitrogen-containing alloy with respect to the nitrogen content of aphosphor to be produced by the secondary nitridation step. The nitrogencontent of the nitrogen-containing alloy after the completion of theprimary nitridation step is naturally smaller than the nitrogen contentof a phosphor. The value of the formula [7] is not limited as long as aphosphor of the present invention is obtained. The value of the formula[7] is usually 0.03 or more, preferably 0.04 or more, more preferably0.05 or more, still more preferably 0.1 or more, and particularlypreferably 0.15 or more, and usually 0.9 or less and preferably 0.85 orless.

When the value of NI/NP of the formula [7] is lower than the rangeabove, the progress of nitridation in the primary nitridation step maybe insufficient. In this case, the heat generation rate in the secondarynitridation step tends to increase, thus resulting in a deterioration inthe performance of a phosphor. When the value of NI/NP of the formula[7] exceeds the range above, the nitrogen-containing alloy is unstable,thus making the handling of the nitrogen-containing alloy difficult.

To smoothly perform the secondary nitridation step, preferably, thedegree of progress of the nitridation of the nitrogen-containing alloy,which is indicated by, for example, the formulae [5], [6], and [7], isappropriately adjusted in response to the reactivity of an alloy as araw material. The reactivity of the alloy as the raw material isdetermined by, for example, the composition and weight-average mediandiameter D₅₀. For example, in the case where the raw material containsSr or has a small weight-average median diameter D₅₀, the raw materialis highly reactive with nitrogen. Thus, in the case of using the highlyreactive raw material, the degree of nitridation in the primarynitridation step is preferably high. In contrast, in the case of using araw material with low reactivity, the degree of nitridation in theprimary nitridation step is preferably low.

The reactivity of an alloy powder, composed of an alloy for a phosphorprecursor, prepared in the milling step with nitrogen can be estimatedby TG-DTA measurement of the alloy powder under a stream of nitrogen.Specifically, the alloy powder is allowed to react with nitrogen underatmospheric pressure in the temperature range from a temperature 100° C.lower than the melting point of the alloy for the phosphor precursor to1,500° C. while the weight of the alloy powder is being monitored byTG-DTA measurement, and then the rate of weight increase is determined.

In this case, there is no problem for the continuous process. In thecase where the batch process is employed, the nitrogen concentration inthe atmosphere in the primary nitridation step is preferably selected insuch a manner the rate of weight increase of the alloy powder is usually5% by weight/hr or more and preferably 10% by weight/hr or more, andusually 300% by weight/hr or less, preferably 150% by weight/hr or less,and particularly preferably 100% by weight/hr or less (provided that theheating rate is set at 10° C./min). In the case of employing the batchprocess, when the nitrogen concentration such that the rate of weightincrease exceeds the range above is selected, an excessively largeexotherm tends to occur in the primary nitridation step. In some cases,heat generated in producing a large amount of a nitrogen-containingalloy causes the fusion or phase separation of the alloy or thedecomposition of a nitride, thereby degrading characteristics of aphosphor. When the nitrogen concentration such that the rate of weightincrease is lower than the range above is selected, for example, anitridation reaction does not proceed adequately. This may cause thereduction in productivity and the brightness of a phosphor.

Meanwhile, the oxygen content of a nitrogen-containing alloy can bedetermined by measuring the amount of oxygen with, for example, anoxygen-nitrogen analyzer (manufactured by Leco Corporation) andcalculating the oxygen content from the formula [8]:

Oxygen content of nitrogen-containing alloy (wt %)=(amount ofoxygen/weight of nitrogen-containing alloy)×100  [8].

The oxygen content (percent by weight) of the nitrogen-containing alloyis not limited as long as a phosphor of the present invention isobtained. The oxygen content is usually 7.5% by weight or less andpreferably 5% by weight or less, and usually 0.1% by weight or more. Anexcessively high oxygen content may cause a reduction in the brightnessof a phosphor produced.

The nitrogen-containing alloy described above is further subjected tonitridation in the secondary nitridation step to provide a phosphor ofthe present invention. Alternatively, a mixture of the powder of anitrogen-containing alloy, an alloy powder (alloy powder before theprimary nitridation step) prepared in the milling step, and the like isfurther subjected to nitridation in the secondary nitridation step toprovide a phosphor of the present invention. In this case, the heatgeneration rate in the secondary nitridation step can be controlled;hence, it is possible to mass-produce a phosphor from such an alloy.

The weight-average median diameter D₅₀ of an alloy powder of anitrogen-containing alloy before the secondary nitridation step ispreferably adjusted in response to the activity of metal elementsconstituting the alloy. A specific range thereof is not limited as longas a phosphor of the present invention is obtained. Usually, theweight-average median diameter D₅₀ preferably has the same range as thealloy powder of the alloy for a phosphor precursor (alloy powder beforethe primary nitridation step).

(Cooling and Milling)

In the case where the primary nitridation step is performed, after thecompletion of the primary nitridation step, the alloy powder prepared inthe primary nitridation step may be cooled (cooling step) before thesecondary nitridation step.

In the case where an apparatus used in the primary nitridation stepdiffers from an apparatus used in the secondary nitridation step,usually, an alloy powder is cooled to 200° C. or lower, taken out, andplaced into the apparatus used in the secondary nitridation step. Alsoin the case where a single apparatus is used in both of the primarynitridation step and the secondary nitridation step, an alloy powder istemporarily cooled before the change or replacement of the atmosphere inthe apparatus. If the cooling is not performed, a sharp change innitrogen partial pressure may cause a sudden rise in the temperature ofthe alloy powder to melt the alloy powder. Furthermore, the alloy powderis likely to be altered by contact with the air at a high temperature.The cooling temperature in this case is usually a temperature equal toor lower than a temperature 100° C. lower than the melting point of thenitrogen-containing alloy and preferably a temperature equal to or lowerthan a temperature 200° C. lower than the melting point of thenitrogen-containing alloy. The lower limit is not particularly limitedbut usually room temperature or higher.

After cooling, milling and/or mixing is performed as needed. Theweight-average median diameter D₅₀ of the alloy powder composed of thenitrogen-containing alloy after milling is usually 100 μm or less and ispreferably comparable to that of the alloy powder before the primarynitridation step.

The nitrogen-containing alloy after the primary nitridation step has ahigh critical oxygen concentration compared with the alloy powder,having the same particle diameter range, before the primary nitridationstep. Thus, the dust explosion is less likely to occur. That is, thenitrogen-containing alloy after the primary nitridation step hasimproved handling and safety. However, the nitrogen-containing alloyafter the primary nitridation step can be hydrolyzed in air orcontaminated with oxygen by oxidation. Thus, the nitrogen-containingalloy after the primary nitridation step is preferably handled in dryair, a nitrogen atmosphere, or in an inert gas atmosphere such as anargon atmosphere. The handling thereof is particularly preferablyperformed in a nitrogen atmosphere. The inert gases may be used alone.Any two or more of the inert gases may be combined in any proportion.

The oxygen concentration in the atmosphere is usually 5% by weight orless and preferably 4% by weight or less, and usually 0.1 ppm or more.An excessively high oxygen concentration may cause oxidation thereof.

Employment of the primary nitridation step results in control of thereactivity between the alloy and nitrogen in the secondary nitridationstep. The amount of a phosphor produced at one time, which variesdepending on other conditions, can be increased to 1.5 or more times andpreferably 2 or more times that in the case where the primarynitridation step is not performed.

<Secondary Nitridation Step (Nitridation Treatment Step)>

In the secondary nitridation step, a raw material for a phosphor issubjected to nitridation treatment to provide a phosphor. In this case,as the raw material for the phosphor, an alloy, not having beensubjected to the primary nitridation step, for a phosphor precursor(preferably, the alloy powder thereof) may be used. Anitrogen-containing alloy (preferably, the alloy powder thereof)prepared in the primary nitridation step may also be used. Furthermore,both of them may be used. From the viewpoint of achieving goodindustrial productivity, preferably, only the alloy powder of thenitrogen-containing alloy or a mixture of the alloy powder of the alloyfor a phosphor precursor and the alloy powder of the nitrogen-containingalloy is subjected to nitridation treatment. Furthermore, in the casewhere the mixture is subjected to the nitridation treatment, preferably,the proportion of the nitrogen-containing alloy powder is 20% by weightor more. The nitrogen-containing alloy preferably has a total content ofmetal elements of 97% by weight or less (corresponding to requirement1)). The whole or part of the alloy for a phosphor precursor isparticularly preferably composed of the nitrogen-containing alloy havinga nitrogen content of 10% by weight or more. At an excessively smallamount of the nitrogen-containing alloy or an excessively low nitrogencontent of the nitrogen-containing alloy, there is a possibility thatthe advantage of the primary nitridation step is not sufficientlyafforded.

The nitridation treatment in the secondary nitridation step is performedby placing a raw material for a phosphor into a firing vessel, such as acrucible or a tray, and heating the raw material under anitrogen-containing atmosphere. Specifically, the nitridation treatmentis performed in accordance with a procedure described below.

The raw material for a phosphor is placed into the firing vessel. Thematerial for the firing vessel used is not limited as long as theadvantage of the production method of the present invention is afforded.Examples of the material include boron nitride, silicon nitride, carbon,aluminum nitride, and tungsten. Among these, boron nitride is preferredbecause of excellent corrosion resistance. These materials may be usedalone or in any combination of two or more thereof in any proportion.

Any shape of the firing vessel used here may be used as long as theadvantage of the production method of the present invention is afforded.Examples of the shape of the bottom of the firing vessel that can beused include shapes having no vertex, such as circles and ellipses, andpolygons, such as triangles and rectangles. The height of the firingvessel is not limited as long as the firing vessel can be placed into afurnace. The height of the firing vessel may be low or high. Inparticular, a shape having good heat dissipation performance ispreferably selected.

The firing vessel into which the raw material for a phosphor is chargedis placed into a firing apparatus (also referred to as a “furnace”). Thefiring apparatus used herein is not limited as long as the advantage ofthe production method of the present invention is afforded. A firingapparatus having the function of controlling the atmosphere in theapparatus is preferred. A firing apparatus also having the function ofcontrolling the pressure is preferred. For example, a hot isostaticpress (HIP) and a resistance-heating vacuum/pressure atmosphereheat-treatment furnace are preferred.

Before the initiation of heating, preferably, a nitrogen-containing gasflows into the firing apparatus to sufficiently replace the atmospherein the system with the nitrogen-containing gas. The system may beevacuated before the nitrogen-containing gas flow, as needed.

Examples of the nitrogen-containing gas used for the nitridationtreatment include gases containing a nitrogen element, e.g., nitrogen,ammonia, and a mixed gas of nitrogen and hydrogen. Thenitrogen-containing gases may be used alone or in any combination of twoor more in any proportion. The oxygen concentration in the system has aneffect on the oxygen content of a phosphor to be produced. A phosphorcontaining too much oxygen would be insufficient in light emissionintensity. Thus, a lower oxygen concentration in an atmosphere used inthe nitridation treatment is preferred. The oxygen concentration isusually 0.1% by volume or less, preferably 100 ppm or less, and morepreferably 10 ppm or less. An oxygen getter such as carbon or molybdenummay be placed at the area of the system to be heated in order to reducethe oxygen concentration, as needed. The oxygen getter may be usedalone. Any two or more of oxygen getters may be combined in anyproportion.

The nitridation treatment is performed by heating a raw material for aphosphor in the system filled with the nitrogen-containing gas or undera stream of the nitrogen-containing gas. The pressure of thenitrogen-containing gas may be slightly lower than, equal to, or higherthan the atmospheric pressure. To prevent the contamination of thesystem with oxygen in air, the pressure is preferably equal to or higherthan the atmospheric pressure. If a furnace used is less airtight, apressure of less than atmospheric pressure may cause the contaminationof the system with a large amount of oxygen and a deterioration in theperformance of a phosphor produced. The gauge pressure of thenitrogen-containing gas is preferably 0.2 MPa or more and morepreferably 10 MPa or more, and preferably 200 MPa or less.

The heating temperature of the raw material for a phosphor is notlimited as long as a phosphor of the present invention is obtained. Theheating temperature is usually 800° C. or higher, preferably 1,000° C.or higher, more preferably 1,200° C. or higher, and usually 2,200° C. orlower, preferably 2,100° C. or lower, and more preferably 2,000° C. orlower. A heating temperature of less than 800° C. may cause an extremelyprolonged period of time required for the nitridation treatment. Aheating temperature exceeding 2,200° C. may cause the evaporation ordecomposition of a nitride formed and thus alter the chemicalcomposition of the resulting nitride phosphor. As a result, the phosphormay have deteriorated characteristics, and the reproducibility of theproduction process may be low.

Furthermore, the heating temperature, which varies depending on thecomposition and the like of the alloy, is a temperature equal to orhigher than a temperature usually 300° C., preferably 400° C., morepreferably 500° C. and particularly preferably 700° C. higher than themelting point of the alloy for a phosphor precursor. The melting pointof the alloy is the same as that in the description for the primarynitridation step.

The heating time (holding time at the maximum temperature) in thenitridation treatment may be equal to the time required for the reactionbetween the raw material for a phosphor and nitrogen. The heating timeis usually 1 minute or more, preferably 10 minutes or more, morepreferably 30 minutes or more, and still more preferably 60 minutes ormore. A heating time of less than 1 minute may cause an incompletenitridation reaction, thereby resulting in a phosphor havingdeteriorated characteristics. The upper limit of the heating timedepends on production efficiency and is usually 24 hours or less.

The nitridation treatment of the raw material for a phosphor results ina phosphor, having a nitride or oxynitride matrix, of the presentinvention.

In the case where a large amount of the raw material for a phosphor issubjected to the nitridation treatment in the secondary nitridation stepat one time, a nitridation reaction may proceed rapidly in response toother conditions, thereby deteriorating characteristics of a phosphor ofthe present invention. In the case where a large amount of the rawmaterial for a phosphor is subjected to heat treatment at one time, theuse of the heating conditions described below further inhibits theprogress of the rapid nitridation reaction, which is preferred.

That is, in the secondary nitridation step, the heating rate is 9°C./min or less in the temperature range from a temperature 100° C. lowerthan the melting point of an alloy for a phosphor precursor to atemperature 30° C. lower than the melting point (hereinafter, alsoreferred to as a “temperature range in which the heating rate isreduced”). The reason the heating rate is reduced in the temperaturerange from a temperature 100° C. lower than the melting point of thealloy heated to a temperature 30° C. lower than the melting point isdescribed below. Note that also in the case where a nitrogen-containingalloy is used in place of the alloy for a phosphor precursor or where analloy for a phosphor precursor and a nitrogen-containing alloy are used,the “melting point of an alloy for a phosphor precursor” represents themelting point of the alloy for a phosphor precursor.

A phosphor is typically synthesized by placing a raw material into afiring vessel, such as a crucible or a tray, and heating the rawmaterial in a furnace. A reduction in the residence time of the rawmaterial for a phosphor in the furnace results in an increase inproductivity. Thus, the heating rate in a temperature range lower thanthe temperature range required for the reaction is preferably maximizedwithin the allowable range of the ability of the furnace and the thermalshock properties of the crucible or the like.

However, in the case where a phosphor is industrially produced using analloy, such as an alloy for a phosphor precursor or anitrogen-containing alloy, serving as a raw material, a high heatingrate may result in the melting of the alloy powder due to heat generatedduring the nitridation, causing the fusion of particles of the alloy. Asa result, a nitridation reaction does not proceed inside the particlesof the alloy because nitrogen gas does not permeate into the inside, insome cases. Thus, the resulting phosphor tends to have a reducedbrightness. In some cases, the resulting phosphor does not emit light.

Provided that the firing vessel has a constant diameter, when a smallamount of the alloy powder is charged, the foregoing phenomenon does notoccur because of high heat dissipation and a small amount of heataccumulated during the nitridation reaction. However, when a largeamount of the raw material for a phosphor is charged, the heatdissipation performance is reduced. Thus, it is desirable to suppressthe exotherm during the nitridation reaction.

Meanwhile, in the case of the synthesis of a phosphor, in particular, anitride phosphor, an expensive reaction apparatus is usually usedbecause the reaction is performed under high temperature and pressure.For the purpose of cost reduction, it is desirable to increase theamount of the raw material for a phosphor in one operation.

Accordingly, in the production method of the present invention, it ispreferred to reduce the heating rate in a specific temperature rangedescribed below (corresponding to requirement 2)). This makes itpossible to inhibit a deterioration in the performance of a phosphor dueto the accumulation of the heat of reaction even when a phosphor isindustrially produced using an alloy, such as an alloy for a phosphorprecursor or a nitrogen-containing alloy, as a raw material. Inparticular, in the case where an alloy for a phosphor precursor containsSr, in some cases, a nitridation reaction proceeds rapidly in thetemperature range from a temperature 100° C. lower than the meltingpoint of the alloy for the phosphor precursor to the melting point,thereby sharply increasing the weight of the raw material. The reductionin heating rate in this temperature range results in the effect ofeliminating such a sharp increase in weight.

The temperature range in which the heating rate is reduced is usually inthe temperature range from a temperature 100° C. lower than the meltingpoint of the alloy for the phosphor precursor to a temperature 30° C.lower than the melting point, preferably from a temperature 150° C.lower than the melting point of the alloy for the phosphor precursor,and more preferably from a temperature 200° C. lower than the meltingpoint, and preferably to the melting point, more preferably to atemperature equal to or higher than a temperature 100° C. higher thanthe melting point.

The temperature 100° C. lower than the melting point of the alloy forthe phosphor precursor indicates an approximate temperature ofinitiation of the nitridation of the alloy for the phosphor precursor.Furthermore, it is often difficult to control the progress of thenitridation reaction by the heating rate in the temperature range from atemperature 30° C. lower than the melting point to the melting pointbecause the nitridation reaction proceeds rapidly.

The “temperature” used in the temperature range from a temperature 100°C. lower than the melting point to a temperature 30° C. lower than themelting point indicates the temperature in the furnace during the heattreatment, i.e., the pre-set temperature of the firing apparatus.

In the temperature range in which the heating rate is reduced, theheating rate is usually 9° C./min or less and preferably 7° C./min orless. A heating rate exceeding the upper limit is liable to lead to theaccumulation of the heat of the rapid reaction, thereby resulting in aphosphor with reduced brightness. The lower limit of the heating rate isnot particularly limited. From the viewpoint of achieving goodproductivity, the lower limit is usually 0.1° C./min or more andpreferably 0.5° C./min or more.

In the temperature range below the temperature 100° C. lower than themelting point of the alloy for the phosphor precursor, the heatingconditions are not particularly limited, and the temperature may beincreased rapidly or slowly. Furthermore, in view of the responsivenessof the temperature control of the furnace, the heating rate may bereduced to 9° C./min or less from a temperature below a temperature 100°C. lower than the melting point of the alloy.

In the case where heating is continued after the temperature reaches thetemperature 30° C. lower than the melting point of the alloy for thephosphor precursor, it is preferred to slowly increase the temperaturealso in the temperature range from the temperature 30° C. lower than themelting point to the melting point. That is, preferably, the heatingrate is, but not particularly limited to, usually 9° C./min or less andparticularly 7° C./min or less, and usually 0.1° C./min or more andparticularly 0.5° C./min or more. In a high temperature range exceedinga temperature 10° C. higher than the melting point, there is noadvantage of the reduction in heating rate. It is thus preferred to setthe heating rate to 10° C./min or more, e.g., 10° C./min to 100° C./min,in this high temperature range to increase productivity.

The melting point of the alloy for the phosphor precursor is the same asthat in the description for the primary nitridation step.

As described above, nitridation of the alloy for the phosphor precursorand/or the nitrogen-containing alloy results in the production of aphosphor of the present invention.

[III] Other Additional Step {Reheating Step}

A phosphor prepared in the secondary nitridation step may be subjectedto a reheating step (reheat treatment) to grow particles, as needed.This may result in particle growth, thereby affording a phosphor havingimproved characteristics, e.g., high light emission intensity.

In this reheating step, the phosphor may be cooled to room temperatureand then heated again. When the reheat treatment is performed, theheating temperature is usually 1,200° C. or higher, preferably 1,300° C.or higher, more preferably 1,400° C. or higher, and particularlypreferably 1,500° C. or higher, and usually 2,200° C. or lower,preferably 2,100° C. or lower, more preferably 2,000° C. or lower,particularly preferably 1,900° C. or lower. Heating at a temperatureless than 1,200° C. is liable to cause the reduction of the effect ofgrowing the particles of the phosphor. Heating at a temperatureexceeding 2,200° C. may result in the decomposition of the phosphor aswell as waste of heating energy. To prevent the decomposition of thephosphor, the pressure of nitrogen partially constituting theatmospheric gas needs to be greatly increased, so that the productioncost tends to be increased.

Preferably, the phosphor is basically reheated in a nitrogen gasatmosphere, an inert gas atmosphere, or a reducing atmosphere. Any oneof inert gases may be used alone. Alternatively, any two or more inertgases may be combined in any proportion. Furthermore, any one ofreducing gases may be used alone. Alternatively, any two or morereducing gases may be combined in any proportion. The oxygenconcentration in the atmosphere is usually 1,000 ppm or less, preferably100 ppm or less, and more preferably 10 ppm or less. The reheattreatment of the phosphor in an oxidizing atmosphere, such as anoxygen-containing gas with an oxygen concentration exceeding 1,000 ppmor air, may cause the oxidation of the phosphor; hence, a targetphosphor may not be obtained. The atmosphere preferably contains a traceamount of oxygen, for example, 0.1 ppm to 10 ppm of oxygen, because thephosphor can be synthesized at a relatively low temperature.

With respect to the pressure conditions during the reheat treatment, toprevent the contamination of the system with oxygen in air, a pressureequal to or higher than atmospheric pressure is preferred. Like theheating step described above, if a firing apparatus is less airtight, anexcessively low pressure may cause the contamination of the system witha large amount of oxygen and a deterioration in the performance of aphosphor produced.

The heating time (holding time at the maximum temperature) in the reheattreatment is usually 1 minute or more, preferably 10 minutes or more,and more preferably 30 minutes or more, and usually 100 hours or less,preferably 24 hours or less, and more preferably 12 hours. Anexcessively short heating time is liable to cause insufficient particlegrowth. An excessively long heating time is liable to cause waste ofheating energy. In some cases, nitrogen may be removed from the surfaceof the phosphor to deteriorate the light emission properties.

{Post-Treatment Step}

The resulting phosphor may be subjected to a post-treatment step, suchas a dispersion step, classification step, a washing step, and a dryingstep, as needed, and then used for various applications.

<Dispersion Step>

In the dispersion step, aggregating phosphor particles due to particlegrowth and sintering in the nitridation step are disintegrated by theapplication of a mechanical force. Examples of a method ofdisintegration include disintegration with a jet mill utilizing a streamof a gas; and disintegration with a ball mill and bead mill using media.

<Classification Step>

The phosphor powder dispersed by the method described above may besubjected to the classification step so as to have an intended particlesize distribution. The classification is performed with a screeningapparatus based on meshes, such as a vibrating screen and a sifter, aninertial classification apparatus such as an air separator, or acentrifuge such as a cyclone separator.

<Washing Step>

In the washing step, after the phosphor is roughly milled with, forexample, a jaw crusher, a stamp mill, or a hammer mill, the resultingcoarse particles of the phosphor are washed with a neutral solution oran acidic solution (hereinafter, also referred to as a “washingmedium”).

The neutral solution used here is preferably water. The type of waterthat can be used is, but not particularly limited to, preferablydesalted water or distilled water. The electric conductivity of waterused is usually 0.0064 mS/m or more, and usually 1 mS/m or less andpreferably 0.5 mS/m or less. The temperature of water used is usuallyequal to room temperature (about 25° C.). Alternatively, the use of warmor hot water preferably having a temperature of 40° C. or higher andmore preferably 50° C. or higher, and preferably 90° C. or lower andmore preferably 80° C. or lower may reduce the number of times ofwashing of the phosphor particles, washing being performed in order toobtain a target phosphor.

The acidic solution is preferably an acidic aqueous solution. The typeof the acidic aqueous solution is not particularly limited, and theacidic aqueous solution may contain one or more mineral acids such ashydrochloric acid and sulfuric acid. The acid concentration of theacidic aqueous solution is usually 0.1 mol/L or more and preferably 0.2mol/L or more, and usually 5 mol/L or less and preferably 2 mol/L orless. The acidic aqueous solution is more preferable than a neutralaqueous solution because the efficiency of removing soluble ions fromthe phosphor can be high. An acid concentration of the acidic aqueoussolution used in the washing step exceeding 5 mol/L may cause thedissolution of surfaces of the phosphor. An acid concentration of theacidic aqueous solution of less than 0.1 mol/L is liable to lead to aninsufficient effect of using acid.

In the present invention, as the acidic solution used for washing, ahighly corrosive acid such as hydrofluoric acid is not necessary.

The washing media may be used alone or in any combination of two or morein any proportion.

A method for washing the phosphor is not particularly limited. Anexample of the method is a method including adding the resultingphosphor particles to the neutral or acidic solution (washing medium),stirring the mixture for a predetermined period of time to form adispersion, and subjecting the phosphor particles to solid-liquidseparation.

A stirring technique used to wash the phosphor is not particularlylimited as long as the phosphor particles are uniformly dispersed. Forexample, a stirrer with a chip or an agitator may be used.

The amount of the washing medium used is not particularly limited. Anexcessively small amount of the washing medium does not result in asufficient washing effect. An excessively large amount of the washingmedium is unreasonable. Thus, the weight of the washing medium used ispreferably 2 or more times and more preferably 5 or more times theweight of the phosphor washed, and preferably 1,000 or less times andmore preferably 100 or less times the weight of the phosphor washed.

The washing time may be a time such that the phosphor is brought intosufficient contact with the washing medium. The washing time is usuallyin the range of one minute to one hour.

A technique for solid-liquid separation between the washing medium andthe phosphor particles is not particularly limited. Examples thereofinclude filtration, centrifugation, and decantation.

The method for washing the phosphor particles is not limited to theforegoing method including stirring the phosphor particles in thewashing medium to form a dispersion and subjecting the dispersion tosolid-liquid separation. For example, a method for exposing the phosphorparticles to a flow of the washing medium may be employed.

A plurality of such washing steps may be performed. In the case wherethe plurality of washing steps are performed, washing with water may becombined with washing with the acidic aqueous solution. In this case, toprevent the acid from remaining on the phosphor, the phosphor ispreferably washed with the acidic aqueous solution and then with water.The phosphor may be washed with water, with the acidic aqueous solution,and then with water.

In the case where the plurality of washing steps are performed, themilling step and/or the classification step may be performed between thewashing steps.

The phosphor is preferably washed until the electric conductivity of asupernatant liquid is reduced to a predetermined value or less, thesupernatant liquid being obtained from the below-describedwater-dispersing test to which the washed phosphor is subjected to.

Specifically, the washed phosphor is disintegrated or milled with a dryball mill as needed. The phosphor particles are classified by sieving orlevigation so as to have an intended weight-average median diameter. Thephosphor particles are stirred in water weighing ten times as much asthe phosphor for a predetermined period of time, e.g., 10 minutes so asto be dispersed. The dispersion is allowed to stand for 1 hour, leadingto spontaneous sedimentation of the phosphor particles having a specificgravity higher than that of water. The supernatant liquid at this pointis measured with regard to its electric conductivity. The washingoperation above is repeated as needed until the electric conductivity ofthe supernatant liquid usually reaches 50 mS/s or less, preferably 10mS/m or less, and more preferably 5 mS/s or less.

The water used for the water-dispersing test is not particularly limitedand is preferably desalted water or distilled water as described for thewashing medium. The electric conductivity is usually 0.0064 mS/m ormore, and usually 1 mS/m or less and preferably 0.5 mS/m or less. Thetemperature of water used for the water-dispersing test is usually roomtemperature (about 25° C.)

The phosphor is washed as described above to further improve thebrightness of the phosphor.

The electric conductivity of the supernatant liquid obtained from thewater-dispersing test of the phosphor may be measured with, for example,a conductivity meter “EC METER CM-30G”, manufactured by DKK-TOACorporation.

When components constituting the phosphor are partially dissolved in thewater to form ions, the electric conductivity of the supernatant liquidobtained from the water-dispersing test of the phosphor is increased.The fact that the electric conductivity of the supernatant liquid is lowindicates that the water-soluble component content of the phosphor islow.

Furthermore, the phosphor is subjected to the washing step, therebyreducing the oxygen content of the phosphor, in some cases. This isprobably because oxygen-containing impurities, for example, hydroxidesformed by the hydrolysis of nitrides with low crystallinity are removedfrom the phosphor.

For example, in a step of washing the phosphor of the present invention,phenomena described below probably occur.

(1) Nitrides with low crystallinity are hydrolyzed into hydroxides suchas Sr(OH)₂, and the hydroxides are dissolved in water. Washing with hotwater or a dilute acid effectively removes these compounds, therebyreducing the electric conductivity. An excessively high acidconcentration in the washing medium or an excessively prolonged periodof time for exposing the phosphor to the acidic aqueous solution maycause the decomposition of the phosphor.

(2) Boron from the boron nitride (BN) crucible used in the heating stepdescribed above forms water-soluble boron-nitrogen-alkaline earthcompounds to contaminate the phosphor. Washing described above resultsin the decomposition and removal of these compounds.

The reason for improvement in luminous efficiency and brightness bywashing is not completely clear but probably is as follows: When thephosphor immediately after firing is exposed to air, the phosphorslightly smells like ammonia. Thus, unreacted or insufficiently reactedportions of the phosphor are decomposed and removed by washing.

<Drying Step>

After the completion of the washing described above, the phosphor isdried in such a manner that no water remains on the phosphor. Theresulting phosphor is provided for use. A specific operation will betaken as an example. After the completion of the washing, the resultingphosphor slurry is dehydrated with, for example, a centrifuge. Theresulting dehydrated cake is placed on a tray for drying. The cake isdried in the temperature range of 100° C. to 200° C. until the watercontent of the cake reaches 0.1% by weight or less. The resulting drycake is slightly disintegrated by, for example, sieving to yield aphosphor.

A phosphor is used in the form of a powder and dispersed in a dispersionmedium, in many cases. To facilitate such a dispersing operation, thephosphor may be subjected to various surface treatments. This is acommon technique made by those skilled in the art. With respect to thephosphor having been subjected to surface treatment, it is appropriatelyunderstood that the phosphor before subjected to the surface treatmentis regarded as the phosphor of the present invention.

[IV] Production of Alloy by Atomization

An alloy for a phosphor precursor and a nitrogen-containing alloy may beproduced by the method described above. Alternatively, an alloy for aphosphor precursor and a nitrogen-containing alloy may be producedthrough the steps (a) to (c) below. This provides an alloy powder,having an angle of repose of 45° or less, for a phosphor precursor(corresponding to requirement 4).

(a) Among metals, Ln, Ca, Sr, M^(II), M^(III), and M^(IV), constitutinga phosphor,

two or more of these metals are melted into a molten alloy containingthese elements (melting step).

(b) The molten alloy is reduced in size in an inert gas (size-reductionstep).

(c) The molten alloy that has been reduced in size is solidified toprovide an alloy powder (solidifying step).

That is, this method includes reducing the molten alloy in size in thegas and solidifying the reduced molten alloy to yield a powder. In thesize-reduction step (b) and the solidifying step (c), the molten alloyis preferably formed into a powder by, for example, a process forspraying the molten alloy, a process for rapidly cooling the moltenalloy with a roll or a gas flow to yield small-sized alloy ribbons, oran atomization process. Among these, the atomization process ispreferably used.

The atomization process represents a process of dropping or discharginga liquid from a nozzle, atomizing the liquid with jet fluid intodroplets, and solidifying the droplets to yield a powder. Examples ofthe atomization process include a water atomization process, a gasatomization process, and a centrifugal atomization process. Among these,a gas atomization process is particularly preferred because of lowcontamination with impurities such as oxygen and the formation ofspherical alloy particles. A “levi-atomization” process may be employedin the present invention. The levi-atomization process means a gasatomization process combined with levitation melting. This process makesit possible to prevent a raw material from coming into contact with acrucible.

For the purpose of producing an alloy for a phosphor precursor, rawmaterial metals or alloys thereof are weighed in the same way as in thedescription of {Weighing of Raw Material}. The raw materials melted inthe same way as in the description of {Melting of Raw Material} toprepare a molten alloy for a phosphor precursor.

The resulting molten alloy is then subjected to the size-reduction step(b). The molten alloy may be subjected to the size-reduction step (b)without other processing. Alternatively, the molten alloy may beprocessed as follows: The molten alloy cooled and cast into an alloyingot. The alloy ingot is melted and then subjected to thesize-reduction step (b).

Furthermore, the size-reduction step (b) and the solidifying step may beperformed in one operation. In particular, in the gas atomizationprocess, the steps can be easily performed in one operation.

The gas atomization process will be taken as an example.

FIG. 4 schematically illustrates an apparatus for atomizing an alloy bythe gas atomization process. In this apparatus shown in FIG. 4, rawmaterial metals and/or alloys thereof are melt in a melting chamber 101provided with an induction coil 102 (as described above, there are twocases: one case in which the raw material metals are melted to prepare amolten alloy, and then the molten alloy is atomized by the gasatomization process without other processing, and the other case inwhich the molten alloy is solidified and cast into an ingot, and thenthe ingot is melted. In the following description of the atomizationprocess, they are simply referred to as a “raw material alloy”). Theresulting molten alloy is allowed to fall from a small hole formed inthe bottom of a crucible 103 arranged in the melting chamber 101 to forma stream or droplets of the molten alloy. Jet blasts of an atomizationgas from injection nozzles 104 are delivered to the falling moltenalloy. The falling molten alloy is successively atomized by the energyof the jet blasts of the atomization gas. The resulting minute dropletsare solidified in an injection chamber 105 to produce an alloy powder.Usually, coarse particles of the resulting alloy powder are directlycollected in a collection chamber 106. Fine particles thereof arecollected with a cyclone 107. A molten-alloy receiver for removingunatomized molten alloy may be arranged in the injection chamber 105.

The pressure in the melting chamber 101 is not limited as long as aphosphor of the present invention is produced. The pressure therein ispreferably in the range of 1×10³ Pa to 1×10⁵ Pa. More preferably, thepressure is equal to or less than atmospheric pressure in view ofsafety. The melting chamber 101 is preferably filled with an inert gasatmosphere in order to prevent the oxidation of the metal. Examples ofthe inert gas include rare gas elements such as helium, neon, and argon.Among these, argon is preferred. These inert gases may be used alone orin any combination of two or more in any proportion.

The material for the crucible 103 is not limited as long as a phosphorof the present invention is produced. Examples of the material that canbe used include aluminum oxide, calcium oxide, magnesium oxide,graphite, and boron nitride. Aluminum oxide or boron nitride ispreferred because it can prevent the contamination with impurities.These materials for the crucible 103 may be used alone or in anycombination of two or more in any proportion.

A method for melting the raw material alloy is not limited. Preferably,the raw material alloy is melted by high-frequency melting in the sameway as in the melting step described in {Melting of Raw Material}. Themolten alloy in the crucible 103 is maintained at a temperature equal toor higher than the solidifying point of the raw material alloy or metal,preferably 1,450° C. or higher and more preferably 1,480° C. or higher,and usually 1,800° C. or lower, preferably 1,700° C. or lower, and morepreferably 1,600° C. or lower by supplying the high-frequency inductioncoil 102 with power.

The injection nozzles 104 are usually composed of a high heat resistanceceramic material. In particular, the injection nozzles 104 arepreferably composed of aluminum oxide, calcium oxide, or boron nitride.The inner diameter of each of the nozzles is appropriately selected inresponse to, for example, the viscosity of the molten alloy. The innerdiameter thereof is usually 0.5 mm or more and preferably 1 mm or more,and usually 5 mm or less and preferably 3 mm or less.

The atomization gas is preferably an inert gas because the gas collidesdirectly with the molten alloy. Among inert gases, nitrogen or a raregas such as argon is preferred. These inert gases may be used alone orin any combination or two or more in any proportion.

The temperature of the atomization gas is not limited but is usuallyequal to room temperature.

The blast pressure of the atomization gas is not limited as long as analloy powder with a desired particle diameters. The blast pressurethereof is usually 10 kg/cm² (0.98 MPa) or more and preferably 20 kg/cm²(1.96 MPa) or more, and usually 100 kg/cm² (9.8 MPa) or less andpreferably 80 kg/cm² (7.84 MPa) or less. A blast pressure outside therange above is liable to cause a reduction in yield.

The injection chamber 105 and the collection chamber 106 are preferablyfilled in an inert gas atmosphere or a nitrogen atmosphere. A nitrogenatmosphere or a nitrogen-containing inert gas atmosphere is morepreferred for economic reasons.

The nitrogen concentration in each of the injection chamber 105 and thecollection chamber 106 is not limited as long as a phosphor of thepresent invention is produced. The nitrogen concentration thereof isusually 0.1% or more, preferably 10% or more, and more preferably 20% ormore, and usually 100% or less. An excessively low nitrogenconcentration may cause the evaporation of highly volatile metalcomponents from surfaces of the particles in the course of atomizationand collection of the resulting alloy powder, thereby changing thesurface composition.

The pressure in each of the injection chamber 105 and the collectionchamber 106 is usually equal to or near atmospheric pressure. Thetemperature in each of the injection chamber 105 and the collectionchamber 106 is not particularly limited as long as the temperature isequal to or lower than the melting point of the alloy for a phosphorprecursor. The temperature in the injection chamber 105 is usually inthe range of 0° C. to 950° C. The temperature in the collection chamber106 is usually 0° C. or higher and preferably 20° C. or higher, andusually 400° C. or lower and preferably 40° C. or lower.

In the solidifying step (c), preferably, the droplets of the moltenalloy formed by the jet fluid are subjected to rapid cooling. The rapidcooling represents an operation of rapidly cooling the molten alloy witha high temperature. The period of time required for solidifying thedroplets of the molten alloy is not limited as long as a phosphor of thepresent invention is produced. The period of time is usually 1 minute orless, preferably 30 seconds or less, more preferably 10 seconds or less,and still more preferably 3 seconds or less. In the gas atomizationprocess described above, the alloy powder is produced by allowing themolten alloy falling through the small hole to collide with theatomization gas to atomize the molten alloy. In this case, from themoment the molten alloy has been atomized into fine particles, each ofthe particles is in a state in which each particle is rapidly cooled bythermal radiation from the surface thereof and the atomization gas. Theparticles can be rapidly solidified because of its large surface areafor dissipating heat with respect to its volume, which is preferred.

In the gas atomization process, in the size-reduction step (b) and thesolidifying step (c), by controlling the atomization gas and/or thenitrogen concentration or the like in the atmosphere in the injectionchamber 105 and the collection chamber 106, the primary nitridation stepproceeds while the alloy powder is being formed, thereby producing anitrogen-containing alloy. In this case, for example, condition i)described below is preferably satisfied. More preferably, bothconditions i) and ii) are satisfied.

i) At least any one of the atomization gas and the atmospheres in theinjection chamber 105 and the collection chamber 106 is anitrogen-containing atmosphere with a high nitrogen concentration. Thenitrogen concentration is preferably close to 100% by volume. Thenitrogen concentration is usually 90% by volume or more, preferably 95%by volume or more, and more preferably 98% by volume or more.

ii) The temperature of each of the injection nozzles 104 and the bottomof the crucible 103 is, which varies depending on the melting point ofthe alloy, usually 900° C. or higher and preferably 1,000° C. or higher,and usually 1,300° C. or lower and preferably 1,200° C. or lower. Inthis case, for example, heating may be performed by high-frequencymelting. Alternatively, the atomizer may be designed so as to thetemperature is achieved by heat conduction from the melting chamber 101.

The resulting alloy powder is subjected to classification treatment, asneeded, and is then subjected to the primary nitridation step and/or thesecondary nitridation step. The resulting alloy powder is screened witha screening apparatus based on meshes, such as a vibrating screen and asifter, an inertial classification apparatus such as an air separator,or a centrifuge such as a cyclone separator so as to have the foregoingdesired value of the weight-average median diameter D₅₀ and desiredparticle size distribution.

Preferably, the classification step is also performed under an inert gasatmosphere. The oxygen concentration in the inert gas atmosphere ispreferably 10% by volume or less and particularly preferably 5% byvolume or less. The type of inert gas is not particularly limited.Usually, gases, such as nitrogen, argon, and helium, may be used aloneor in combination of two or more thereof. From the viewpoint ofachieving good economy, nitrogen is particularly preferable.

As described above, the powder of the alloy for a phosphor precursor orthe powder of the nitrogen-containing alloy is prepared also by theatomization process and the like. According to this process, inparticular, (a) since the molten alloy obtained in the melting step isatomized, every steps of a procedure, from the raw material metals toproduction of the alloy powder and the nitrogen-containing alloy, can becontinuously performed. Furthermore, by arranging a transportation means(e.g., a pipeline or a conveyor belt) configured to transport theresulting alloy powder and/or nitrogen-containing alloy to a firingapparatus used in the secondary nitridation step, every steps of aprocedure, from the raw material metals to the production of a phosphor,can be successively performed.

[V] Characteristics of Alloy Powder Prepared by Atomization Process orthe Like

The alloy powder (powder of the alloy for a phosphor precursor or thenitrogen-containing alloy) prepared by the atomization process or thelike described in item [IV] preferably has characteristics describedbelow.

Flowability

The angle of repose, a collapse angle, and a difference angle are usedas indices of flowability. These angles can be measured by a methoddescribed in Carr et al, Chemical Engineering, January 18,(1965)166-167. For example, these angles can be measured with, forexample, a powder tester (Model PT-N, manufactured by Hosokawa MicronCorporation).

The angle of repose is an angle defined by the horizontal plane and thegeneratrix of a conical pile formed by gently pouring a granularmaterial onto a horizontal surface from a funnel or the like.

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the angle of repose thereof is usually 45° or less(corresponding to requirement 4)), preferably 40° or less, and morepreferably 35° or less. A lower angle of repose is more preferredbecause a lower angle of repose results in higher flowability, thusproviding better handleability in industrial operations. An excessivelyhigh angle of repose is liable to cause low flowability, thus makingtransportation and transfer difficult.

The collapse angle is the slope angle of a pile left after apredetermined impact is applied to a granular material constituting aconical pile with the angle of repose to collapse the pile.

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the collapse angle is usually 25° or less, preferably20° or less, and more preferably 15° or less. A lower collapse angle ismore preferred.

The difference angle is an angle obtained by subtracting the collapseangle from the angle of repose.

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the difference angle is preferably 20° or less. Anexcessively high difference angle is liable to cause a flushingphenomenon, thus making the control difficult, which is not preferred.

The use of an alloy powder having a low angle of repose, a low collapseangle, a low difference angle, and high flowability as a raw materialresults in improvement in handling, so that transportation and transferare improved.

Shape

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, with respect to the shape of the alloy particles,average circularity can be used as a numerical index of sphericity.

The average circularity is determined with the formula described belowand indicates the degree of approximation of the shape of each particlein a projection view to the corresponding perfect circle:

Average circularity=perimeter of perfect circle with area equal toprojected area of particle/perimeter of particle in projection view.

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the average circularity is usually 0.7 or more,preferably 0.8 or more, and more preferably 0.9 or more. An averagecircularity closer to 1 is more preferred.

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the proportion of the number of spherical alloyparticles each having an average circularity of 0.9 or more is usually20% or more and preferably 40% or more.

Weight-Average Median Diameter D₅₀

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the weight-average median diameter D₅₀ needs to beadjusted in response to the activity of metal elements constituting thealloy powder and is usually 0.1 μm or more, preferably 1 μm or more, andmore preferably 3 μm or more, and 100 μm or less, preferably 50 μm orless, and more preferably 30 μm or less. Furthermore, when the alloypowder contains Sr, the weight-average median diameter D₅₀ is usually 5μm or more, preferably 8 μm or more, more preferably 10 μm or more, andparticularly preferably 13 μm or more because of high reactivity withthe atmospheric gas.

A weight-average median diameter D₅₀ lower than the range above maycause an increase in heat generation rate during a reaction such asnitridation, thereby making the control of the reaction difficult. Aweight-average median diameter D₅₀ higher than the range above may leadto an inadequate reaction such as nitridation inside the alloyparticles, thereby reducing the brightness.

Tap Density

Tap density is the density of a specimen that has been subjected tospecific vibrations (tapping). In this specification, the tap density ismeasured below.

About 10 g of an alloy powder is placed into a 10-mL glass graduatedcylinder. The cylinder is manually tapped on a table from a height ofabout 1 cm to 5 cm at about 50 times/min to 500 times/min until thevolume of the powder is not changed (usually 200 times to 800 times).Then the volume (V) of the alloy powder is measured. The tare weight ofthe graduated cylinder is subtracted from the total weight to determinethe net weight (W) of the alloy powder. The value calculated with theformula [9] described below is referred to as a tap density:

Tap density (g/mL)=W (g)/V (mL)  [9].

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the tap density is usually 1.9 g/mL or more andpreferably 2 g/mL or more, and usually 4 g/mL or less and preferably 3g/mL or less. An excessively low tap density may result in difficulty incharging the alloy powder into a reaction vessel in the production of aphosphor, thereby reducing the productivity. An excessively high tapdensity may cause a reduction in the contact efficiency between thealloy particles and an atmosphere such as nitrogen in the firing step.

Oxygen Content and Carbon Content

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the oxygen content is usually 2% by weight or less andpreferably 1% by weight or less. The lower limit is usually 0.05% byweight or more and preferably 0.1% by weight or more.

In the case where an alloy powder for a phosphor precursor used in thepresent invention is prepared by the atomization process or the likedescribed above, the carbon content is 0.2% by weight or less andpreferably 0.1% by weight or less.

Oxygen and carbon contents of the alloy powder outside the ranges aboveare liable to cause a reduction in light emission properties of aphosphor produced, which is not preferred.

The atomization of the alloy by the gas atomization process or the likedescribed above results in a reduction in impurities compared with thecase where the alloy is mechanically milled with a jet mill or the like.The use of the alloy powder with a low impurity content as a rawmaterial advantageously results in improvement in the brightness of aphosphor produced.

The atomization of the alloy by the gas atomization process describedabove results in an alloy powder having a uniform microstructure becausethe homogeneous molten alloy is instantaneously formed into dropletsthat are rapidly cooled. Furthermore, since the droplets arecontinuously formed from the same molten alloy, advantageously, theresulting alloy powder has a negligible difference in compositionbetween particles. Moreover, the alloy powder has high flowability and alow impurity content.

[VI] Mixing of Alloy Powder with Nitride or Oxynitride

In the primary nitridation step and/or the secondary nitridation step,an alloy intended to be subjected to nitridation (i.e., an alloy for aphosphor precursor and/or a nitrogen-containing alloy) may be heated inthe presence of a nitride or an oxynitride. Alternatively, preferably,the alloy intended to be subjected to nitridation is mixed with anitride or an oxynitride, and then the resulting mixture is heated(corresponding to requirement 3)). As the nitride or oxynitride, anitride or an oxynitride containing one or two or more metal elementsconstituting a phosphor of the present invention (hereinafter, alsoreferred to as a “raw material nitride”) is used.

The composition of the raw material nitride is not particularly limitedas long as the raw material nitride and the like are combined with theraw material alloy described above to achieve a target phosphorcomposition. Thus, the raw material nitride preferably contains atetravalent metal element M⁴ containing at least Si in the same way asthe composition of the phosphor described above. More preferably, theraw material nitride further contains one or more metal elements otherthan Si. Still more preferably, the raw material nitride contains anactivating element M₁, a divalent metal element M², and the tetravalentmetal element M⁴. The divalent metal element M² is preferably analkaline-earth metal element. To obtain a uniform phosphor, the rawmaterial nitride preferably contains constituent elements identical tothose of a target phosphor. For example, the raw material nitridepreferably has a composition represented by the general formula [1].More preferably, the raw material nitride has a composition representedby the general formula [2].

Specific examples of the raw material nitride include nitrides ofelements constituting phosphors, e.g., AlN, Si₃N₄, Ca₃N₂, Sr₃N₂, andEuN; complex nitrides of elements constituting phosphors, e.g.,CaAlSiN₃, (Sr,Ca)AlSiN₃, (Sr,Ca)₂Si₅N₈, and SrSiN₂; and complex nitridescontaining activating elements, e.g., (Sr,Ca)AlSiN₃:Eu,(Sr,Ca)AlSiN₃:Ce, (Sr,Ca)₂Si₅N₈:Eu, SrSiN₂:Eu, andSr_(1-x)Ca_(x)Si₂O₂N₂:Eu. These raw material nitrides may be used aloneor in any combination or two or more in any proportion.

The raw material nitride may contain a trace amount of oxygen. The ratioof oxygen to (oxygen+nitrogen) in the raw material nitride is notlimited as long as a phosphor of the present invention is obtained. Theratio thereof is usually 0.5 or less, preferably 0.3 or less, andparticularly preferably 0.2 or less. An excessively high proportion ofoxygen in the raw material nitride may cause a reduction in brightness.

The weight-average median diameter D₅₀ of the raw material nitride isnot limited as long as the raw material nitride is mixed with othermaterials without a hitch. Preferably, the raw material nitride iseasily mixed with other materials. For example, the weight-averagemedian diameter D₅₀ of the raw material nitride is preferably comparableto that of the alloy powder. The specific value of the weight-averagemedian diameter D₅₀ of the raw material nitride is not limited as longas a phosphor is obtained. The weight-average median diameter D₅₀ ispreferably 200 μm or less, more preferably 100 μm or less, particularlypreferably 80 μm or less, and still more preferably 60 μm or less, andpreferably 0.1 μm or more and more preferably 0.5 μm or more.

The mixing ratio of the raw material nitride to the total amount of theraw materials for a phosphor, i.e., the mixing ratio of the raw materialnitride to the total amount of the alloy (alloy powder of the alloy fora phosphor precursor and/or the nitrogen-containing alloy) and the rawmaterial nitride, is usually 1% by weight or more, preferably 5% byweight or more, more preferably 10% by weight or more, and still morepreferably 15% by weight or more. An excessively low mixing ratio of theraw material nitride is liable to lead to an insufficient effect ofimproving the brightness of a phosphor produced. The upper limit of themixing ratio of the raw material nitride is not particularly limited. Anexcessively high mixing ratio of the raw material nitride has a tendencyto lead to improvement in the brightness of a phosphor produced but areduction in productivity. Thus, the upper limit is usually 85% byweight or less.

The incorporation of the raw material nitride in the alloy in theprimary nitridation step and/or the secondary nitridation step resultsin a reduction in heat generation rate per unit volume during thenitridation, thereby inhibiting the occurrence of phenomena in which thegenerated heat causes melting and phase separation of the raw materialand decomposition of the resulting nitride to degrade the properties ofa phosphor produced.

For example, in the case where a phosphor of the present invention isproduced using an alloy powder serving as a raw material, the melting ofthe alloy powder due to heat generated during the nitridation in thesecondary nitridation step may cause the fusion of particles of thealloy, so that a nitridation reaction does not proceed inside theparticles of the alloy because nitrogen gas does not permeate throughthe inside. Thus, the resulting phosphor tends to have a reducedbrightness. In some cases, the resulting phosphor does not emit light.Accordingly, the raw material nitride is incorporated in the alloypowder to overcome the foregoing problems.

Provided that a firing vessel has a constant diameter, when a smallamount of the alloy powder is charged, the phenomena in which thegenerated heat causes melting and phase separation of the raw materialand decomposition of the nitride or oxynitride do not occur because ofhigh heat dissipation and a small amount of heat accumulated during thenitridation reaction. However, the phosphor is synthesized by reactionunder high temperature, leading to large energy consumption. Thus, anincrease in the amount of the alloy powder charged at one time ispreferred for the purpose of cost reduction. A large amount of alloypowder charged into the firing vessel causes a reduction in heatdissipation performance, thereby possibly resulting in the melting andphase separation of the alloy due to the generated heat and thedecomposition of the nitride or oxynitride.

In contrast, the incorporation of the raw material nitride in the alloyin the primary nitridation step and/or the secondary nitridation stepresults in an increase in the amount of the alloy charged into areaction vessel for nitridation while the amount of heat is beingsuppressed, thereby efficiently performing the nitridation treatment.The reason for this is described below. The melting point of the nitrideor oxynitride is usually higher than the alloy. Thus, it is speculatedthat the incorporation of the raw material nitride in the alloy resultsin improvement in the heat dissipation performance of the whole of theraw materials for the phosphor. Hence, the melting of the alloy duringthe nitridation is inhibited to allow the nitridation reaction toproceed smoothly, thereby resulting in a high-performance phosphor withhigh productivity.

[Phosphor]

A phosphor produced by the production method of the present invention(hereinafter, also referred to as a “phosphor of the present invention”)will be described below. As the phosphor of the present invention, aphosphor having a nitride or oxynitride matrix is preferred.

In this specification, the matrix of the phosphor means a crystal orglass (amorphous) with which an activating element can form a solidsolution and also includes a crystal or glass (amorphous) capable ofemitting light without an activating element.

{Composition of Phosphor}

The composition of the phosphor of the present invention is notparticularly limited as long as the phosphor is produced by theproduction method of the present invention. Preferably, the phosphor ofthe present invention contains the tetravalent metal element M⁴containing at least Si and one or more metal elements other than Si.More preferably, the phosphor of the present invention further containsthe activating element M¹. The metal elements other than Si arepreferably alkali-earth metal elements.

The phosphor of the present invention preferably contains the activatingelement M¹, the divalent metal element M², and the tetravalent metalelement M⁴ containing at least Si. More preferably, the phosphor of thepresent invention contains the activating element M¹, the divalent metalelement M², the trivalent metal element M³, and the tetravalent metalelement M⁴ containing at least Si.

As the activating element M¹, various luminescent ions that can beincorporated in a crystalline matrix constituting the phosphor havingthe nitride or oxynitride matrix may be used. The use of at least oneelement selected from the group consisting of Cr, Mn, Fe, Ce, Pr, Nd,Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb results in the production of aphosphor with high light emission properties and is thus preferred.

Preferably, the activating element M¹ contains one or two or moreelements selected from Mn, Ce, Pr, and Eu. More preferably, theactivating element M¹ contains Ce and/or Eu because a phosphor emittingred or yellow light with a high brightness is obtained. To enhance thebrightness and provide various functions such as a light-accumulatingfunction, the activating element M¹ may further contain one or moreco-activating agents in addition to Ce and/or Eu.

In addition to the activating element M¹, various divalent, trivalent,and tetravalent metal elements may be used. To obtain a phosphor withexcellent light emission properties, it is preferred that the divalentmetal element M² be one or more elements selected from the groupconsisting of Mg, Ca, Sr, Ba, and Zn, the trivalent metal element M³ beone or more elements selected from the group consisting of Al, Ga, In,and Sc, and the tetravalent metal element M⁴ be one or more elementsselected from the group consisting of Si, Ge, Sn, Ti, Zr, and Hf.

Furthermore, a composition in which Ca and/or Sr accounts for 50% bymole or more of the divalent metal element M² results in a phosphor withexcellent light emission properties and is thus preferred. Morepreferably Ca and/or Sr accounts for 80% by mole or more of the divalentmetal element M², even more preferably accounts for 90% by mole or morethereof, and the most preferably accounts for 100% by mole thereof.

Moreover, a composition in which Al accounts for 50% by mole or more ofthe trivalent metal element M³ results in a phosphor with excellentlight emission properties and is thus preferable. More preferably Alaccounts for 80% by mole or more of the trivalent metal element M³, evenmore preferably accounts for 90% by mole or more thereof, and the mostpreferably accounts for 100% by mole thereof.

Additionally, a composition in which Si accounts for 50% by mole or moreof the tetravalent metal element M⁴ containing at least Si results in aphosphor with excellent light emission properties and is thuspreferable. More preferably Si accounts for 80% by mole or more of thetetravalent metal element M⁴ containing at least Si, even morepreferably accounts for 90% by mole or more thereof, and the mostpreferably accounts for 100% by mole thereof.

The composition in which Ca and/or Sr accounts for 50% by mole or moreof the divalent metal element M², Al accounts for 50% by mole or more ofthe trivalent metal element M³, and Si accounts for 50% by mole or moreof the tetravalent metal element M⁴ containing at least Si results in aphosphor with markedly excellent light emission properties and is thusparticularly preferable.

A phosphor of the present invention preferably has a chemicalcomposition of the general formula [1]:

M¹ _(a)M² _(b)M³ _(c)M⁴ _(d)N_(e)O_(f)  [1]

wherein a, b, c, d, e, and f are values satisfying the followingrequirements:

0.00001≦a≦0.15,

a+b=1,

0.5≦c≦1.5,

0.5≦d≦1.5,

2.5≦e≦3.5, and

0≦f≦0.5,

wherein in the general formula [1], M¹ represents the activating elementM¹, M² represents the divalent metal element M², M³ represents thetrivalent metal element M³, and M⁴ represents the tetravalent metalelement M⁴ containing at least Si.

The reasons why the values a to f in the general formula [1] arepreferably within the ranges above are described below.

A value a of less than 0.00001 is liable to lead to insufficient lightemission intensity. A value a exceeding 0.15 is liable to lead to a highconcentration quenching effect to reduce the light emission intensity.Thus, raw materials are preferably formulated in such a manner that thevalue a is usually 0.00001 or more, preferably 0.0001 or more, morepreferably 0.001 or more, still more preferably 0.002 or more, andparticularly preferably 0.004 or more, and usually 0.15 or less,preferably 0.1 or less, more preferably 0.05 or less, still morepreferably 0.04 or less, and particularly preferably 0.02 or less.

The composition of a mixture of raw materials is adjusted in such amanner that the sum of the values a and b is usually 1 because atomicsites of the divalent metal element M² are replaced with the activatingelement M¹ in the crystalline matrix of the phosphor.

A value c of less than 0.5 or a value c exceeding 1.5 is liable to leadto the formation of a heterogeneous phase in the production and areduction in the yield of the phosphor. Also from the viewpoint ofachieving a good light emission intensity, therefore, the raw materialsare preferably formulated in such a manner that the value c is usually0.5 or more, preferably 0.6 or more, and more preferably 0.8 or more,and usually 1.5 or less, preferably 1.4 or less, and more preferably 1.2or less.

A value d of less than 0.5 or a value d exceeding 1.5 is liable to leadto the formation of a heterogeneous phase in the production and areduction in the yield of the phosphor. Also from the viewpoint ofachieving a good light emission intensity, therefore, the raw materialsare preferably formulated in such a manner that the value d is usually0.5 or more, preferably 0.6 or more, and more preferably 0.8 or more,and usually 1.5 or less, preferably 1.4 or less, and more preferably 1.2or less.

The value e is a coefficient that indicates the nitrogen content andexpressed as the following equation:

$\begin{matrix}{e = {\frac{2}{3} + c + {\frac{4}{3}d}}} & \left\lbrack {{Exp}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

Substitution of the requirements 0.5≦c≦1.5 and 0.5≦d≦1.5 into thisexpression yields:

1.84≦e≦4.17.

In the composition of the phosphor represented by the general formula[1], however, a value e, which represents the nitrogen content, of lessthan 2.5 is liable to cause a reduction in the yield of the phosphor.Furthermore, a value e exceeding 3.5 is also liable to cause a reductionin the yield of the phosphor. Hence, the value e is usually 2.5≦e≦3.5.

Oxygen in the phosphor represented by the general formula [1] probablyresults from oxygen contained as an impurity in raw material metals,oxygen introduced in the production process including, for example, themilling step and the nitridation step, and the like. The value findicating the oxygen content is preferably in the range of 0 to 0.5 aslong as decreases in light emission properties of the resulting phosphorare at acceptable levels.

Among the phosphors represented by the general formula [1], a phosphormay have a composition of the general formula [2]:

M^(1′) _(a′)Sr_(b′)Ca_(c′)M^(2′) _(d′)Al_(e′)Si_(f′)N_(g′)  [2]

Wherein a′, b′, c′, d′, e′, f′, and g′ are values satisfying thefollowing requirements:

0.00001≦a′≦0.15,

0.1≦b′≦0.99999,

0≦c′≦1,

0≦d′≦1,

a′+b′+c′+d′=1,

0.5≦e′≦1.5,

0.5≦f′≦1.5,

0.8×(2/3+e′+4/3×f′)≦g′≦1.2×(2/3+e′+4/3×f′).

M^(1′) represents an activating element selected from a group consistingof Cr, Mn, Fe, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb in thesame way as M¹ in the general formula [1]. Preferably, the activatingelement M^(1′) contains one or two or more elements selected from Mn,Ce, Pr, and Eu. Particularly preferably, the activating element M^(1′)contains Ce and/or Eu.

M^(2′) represents Mg and/or Ba, preferably Mg. The incorporation of Mgresults in a phosphor with an emission peak at a longer wavelength.

The value a′ is usually 0.00001 or more, preferably 0.001 or more, andmore preferably 0.002 or more, and usually 0.15 or less, preferably 0.05or less, and more preferably 0.01 or less.

The value b′ is usually 0.1 or more, 0.4 or more, and more preferably0.7 or more, and usually 0.99999 or less.

The value c′ is usually 0 or more, and usually less than 1, preferably0.5 or less, and more preferably 0.3 or less.

The value d′ is usually 0 or more, and usually less than 1, preferably0.5 or less, and more preferably 0.2 or less.

The relationship among a′, b′, c′, and d′ usually satisfies

a′+b′+c′+d′=1.

The value e′ is usually 0.5 or more, preferably 0.8 or more, and morepreferably 0.9 or more, and usually 1.5 or less, preferably 1.2 or less,and more preferably 1.1 or less.

The value f′ is usually 0.5 or more, preferably 0.8 or more, and morepreferably 0.9 or more, and usually 1.5 or less, preferably 1.2 or less,and more preferably 1.1 or less.

The value g′ is usually 0.8×(2/3+e′+4/3×f′) or more, preferably0.9×(2/3+e′+4/3×f′) or more, more preferably 2.5 or more, and usually1.2×(2/3+e′+4/3×f′) or less, preferably 1.1×(2/3+e′+4/3×f′) or less, andmore preferably 3.5 or less.

Hereinafter, a phosphor in which the value b′ in the general formula [2]is in the range of 0.4 to 0.99999 and the value d′ is zero is referredto as a “phosphor having a high Sr content”, in some cased.

Oxygen contained in the phosphor of the present invention probablyresults from oxygen contained as an impurity in raw material metals, thecontamination in the production process including, for example, themilling step and the nitridation step, and the like.

The oxygen content is usually 5% by weight or less, preferably 2% byweight or less, and most preferably 1% by weight or less as long asdecreases in light emission properties of the resulting phosphor are atacceptable levels.

Specific examples of the composition of the phosphor include(Sr,Ca,Mg)AlSiN₃:Eu, (Sr,Ca,Mg)AlSiN₃:Ce, (Sr,Ca,Ba)₂Si₅N₈:Eu, and(Sr,Ca,Ba)₂Si₅N₈:Ce

[Properties of Phosphor]

A phosphor produced in the present invention may have propertiesdescribed below.

<Emission Color>

The phosphor of the present invention can emit light with an intendedemission color, e.g., blue, blue green, green, yellow green, yellow,orange, or red, by adjusting, for example, the chemical composition.

Emission Spectrum

For example, in the case where the phosphor of the present invention isthe phosphor having a high Sr content and containing Eu serving as theactivating element M¹, when the emission spectrum of the phosphor ismeasured by exciting the phosphor by light having a peak wavelength of465 nm in view of applications as orange to red phosphors, the phosphorpreferably has characteristics described below.

The peak wavelength λp (nm) in the emission spectrum of the phosphor isusually more than 590 nm and preferably 600 nm or more, and usually 650nm or less and preferably 640 nm or less. When the peak emissionwavelength λp is excessively short, the light emitted from the phosphortends to be yellowish. When the peak emission wavelength λp isexcessively long, the light emitted from the phosphor tends to be darkreddish. Both cases are not preferred because the phosphor can emitlight with reduced properties as orange to red light.

In the phosphor described above, the full width at half maximum(hereinafter, appropriately referred to as “FWHM”) of the emission peakin the emission spectrum is usually more than 50 nm, preferably 70 nm ormore, and more preferably 75 nm or more, and usually less than 120 nm,preferably 100 nm or less, and more preferably 90 nm or less. Anexcessively narrow FWHM may cause a reduction in light emissionintensity. An excessively wide FWHM may cause a reduction in colorpurity.

To excite the phosphor described above by light having a peak wavelengthof 465 nm, for example, a GaN-based light-emitting diode can be used.The emission spectrum of the phosphor of the present invention can bemeasured with, for example, a fluorescence spectrometer (manufactured byJASCO Corporation) including a 150-W xenon lamp as an excitation lightsource and a CCD multichannel detector C7041 (manufactured by HamamatsuPhotonics K.K.) as a spectrometer. The peak emission wavelength and thefull width at half maximum of the emission peak can be calculated fromthe resulting emission spectrum.

Weight-Average Median Diameter D₅₀

The weight-average median diameter D₅₀ of the phosphor of the presentinvention is usually 3 μm or more and preferably 5 μm or more, andusually 30 μm or less and preferably 20 μm or less. An excessively smallweight-average median diameter D₅₀ may cause a reduction in brightnessand lead to aggregation of the phosphor particles. An excessively largeweight-average median diameter D₅₀ is liable to cause an uneven coatingand clogging of a dispenser or the like.

The weight-average median diameter D₅₀ in the present invention can bemeasured with, for example, a laser diffraction-scattering particle sizedistribution analyzer.

Temperature Characteristics

The phosphor of the present invention also has excellent temperaturecharacteristics. Specifically, in the case where the phosphor isirradiated with light having an emission peak at a wavelength of 455 nm,the ratio of the peak emission intensity at 150° C. in the emissionspectrum to the peak emission intensity at 25° C. in the emissionspectrum is usually 55% or more, preferably 60% or more, andparticularly preferably 70% or more.

The ratio is less likely to exceed 100% because the light emissionintensity of a typical phosphor decreases with increasing temperature.The ratio may exceed 100% for any reason. However, a ratio exceeding150% is liable to lead to a color shift due to a change in temperature.

The phosphor of the present invention has excellent temperaturecharacteristics with regard to its brightness as well as its peakemission intensity described above. Specifically, in the case where thephosphor is irradiated with light having an emission peak at awavelength of 455 nm, the ratio of the brightness at 150° C. to thebrightness at 25° C. is usually 55% or more, preferably 60% or more, andparticularly preferably 70% or more.

The temperature characteristics are measured as described below using,for example, an apparatus including a multichannel spectrophotometerMCPD7000 (manufactured by Otsuka Electronics Co., Ltd.) serving as anemission spectrometer, a luminance colorimeter BM5A serving as abrightness measuring apparatus, a 150-W xenon lamp serving as a lightsource, and a stage having a cooling mechanism with a Peltier elementand a heating mechanism with a heater. A cell containing a phosphorsample is placed on the stage. The temperature is changed in the rangeof 20° C. to 150° C. The surface of the phosphor should be maintained ata constant measurement temperature. The phosphor was excited by lighthaving a peak wavelength of 455 nm obtained by dispersing light from thelight source with a diffraction grating, and an emission spectrum ismeasured. The emission peak intensity is determined from the measuredemission spectrum. The measurements of the surface temperature of thephosphor are corrected using values of the temperature measured with aradiation thermometer and a thermocouple.

Other Properties

The phosphor of the present invention preferably has higher internalquantum efficiency. The internal quantum efficiency is usually 0.5 ormore, preferably 0.6 or more, and more preferably 0.7 or more. Lowinternal quantum efficiency is liable to cause a reduction in luminousefficiency and thus is not preferred.

The phosphor of the present invention preferably has higher absorptionefficiency. The absorption efficiency is usually 0.5 or more, preferably0.6 or more, and more preferably 0.7 or more. Low absorption efficiencyis liable to cause a reduction in luminous efficiency and thus is notpreferred.

{Application of Phosphor}

The phosphor of the present invention has advantageous properties suchas high brightness and high color rendering properties and therefore issuitable for various light-emitting devices (“light-emitting devices ofthe present invention” described below). In the case where the phosphorof the present invention is an orange or red phosphor, for example, acombination of the phosphor of the present invention, a green phosphor,and a blue phosphor results in a white-light-emitting device with highcolor rendering properties. Such a light-emitting device can be used asa lighting system or a light-emitting section (in particular, abacklight for liquid crystal devices) of a display. The phosphor of thepresent invention can be used alone. For example, a combination of anear-ultraviolet LED and the orange phosphor of the present inventionresults in an orange-light-emitting device.

{Phosphor-Containing Composition}

A mixture of the phosphor of the present invention and a liquid mediummay also be used. In particular, in the case where the phosphor of thepresent invention is used for applications such as a light-emittingdevice, a dispersion of the phosphor dispersed in the liquid medium ispreferably used. The dispersion of the phosphor of the present inventiondispersed in the liquid medium is appropriately referred to as a“phosphor-containing composition of the present invention”.

<Phosphor>

The type of phosphor of the present invention incorporated in thephosphor-containing composition of the present invention is not limited.Any phosphor described above may be selected. The phosphor-containingcomposition of the present invention may contain only one phosphor ofthe present invention. Alternatively, the phosphor-containingcomposition of the present invention may contain any two or more typesof phosphors in any proportion. Furthermore, the phosphor-containingcomposition of the present invention may contain a phosphor differentfrom the phosphor of the present invention, as needed.

<Liquid Medium>

The liquid medium used for the phosphor-containing composition of thepresent invention is not particularly limited as long as the desiredperformance of the phosphor is not impaired. For example, any inorganicmaterial and/or organic material may be used as long as, for example,the liquid medium is liquid under intended conditions of use, suitablydisperses the phosphor of the present invention, and does not produce anunfavorable reaction.

Examples of the inorganic material include solutions each prepared byhydrolytic polymerization of a metal alkoxide, a ceramic precursorpolymer, or a solution containing a metal alkoxide by a sol-gel method;and inorganic materials each prepared by solidifying a combination ofthese materials (e.g., an inorganic material having a siloxane bond).

Examples of the organic material include thermoplastic resins,thermosetting resins, and photocurable resins. Specific examples thereofinclude methacrylic resins such as polymethyl methacrylate; styreneresins such as polystyrene and styrene-acrylonitrile copolymers;polycarbonate resins; polyester resins; phenoxy resins; butyral resins;polyvinyl alcohol; cellulose resins, such as ethyl cellulose, celluloseacetate, and cellulose acetate butyrate; epoxy resins; phenolic resins;and silicone resins.

Among these materials, when the phosphor is used in a high-powerlight-emitting device such as an illuminator, a silicon-containingcompound may be preferably used from the viewpoint of achieving goodheat resistance, light resistance, and the like.

The silicon-containing compound means a compound having a silicon atomin its molecule. Examples thereof include organic materials such aspolyorganosiloxanes (silicone materials); inorganic materials, such assilicon oxide, silicon nitride, and silicon oxynitride; glass materials,such as borosilicates, phosphosilicates, and alkali silicates. Amongthese materials, a silicone material is preferred from the viewpoint ofease of handling and the like.

The silicone material usually indicates an organic polymer having a mainchain composed of siloxane bonds. Examples thereof include compoundsrepresented by the formula (i) and mixtures thereof.

[Chem. 1]

(R¹R²R³SiO_(1/2))_(M)(R⁴R⁵SiO_(2/2))_(D)(R⁶SiO_(3/2))_(T)(SiO_(4/2))_(Q)  formula(i)

In the formula (i), R¹ to R⁶ may be the same or different, and each areselected from the group consisting of organic functional groups, ahydroxy group, a hydrogen atom.

Furthermore, in the formula (i), M, D, T, and Q each represent a valueof 0 or more and less than 1 and satisfy M+D+T+Q=1.

In the case where the silicone material is used to seal a semiconductorlight-emitting element that can be used as a first illuminant describedbelow, after sealing is performed with a liquid silicone material, theliquid silicone material can be cured by heat or light.

When silicone materials are categorized on the basis of curingmechanisms, typical examples thereof include addition polymerizationcuring-type, condensation polymerization curing-type, ultraviolet raycuring-type, and peroxide curing-type silicone materials. Among thesematerials, addition polymerization curing-type silicone materials(addition-type silicone resins), condensation curing-type siliconematerials (condensation-type silicone resins), and ultraviolet raycuring-type silicone materials are preferred. Addition-type siliconematerials and condensation silicone materials will be described below.

Addition-type silicone materials indicate silicone materials havingpolyorganosiloxane chains crosslinked by organic additional bonds. Atypical example thereof is a compound having Si—C—C—Si bonds atcrosslinking sites, the Si—C—C—Si bonds being obtained by reaction ofvinylsilane with hydrosilane in the presence of an addition-typecatalyst such as a Pt catalyst. These materials can be commerciallyavailable. Examples of specific trade names of additionpolymerization-type silicone materials include LPS-1400, LPS-2410, andLPS-3400 manufactured by Shin-Etsu Chemical Co. Ltd.

Condensation-type silicone materials indicate, for example, compoundshaving Si—O—Si bonds at crosslinking sites, the Si—O—Si bonds beingobtained by hydrolysis and polycondensation of alkylalkoxysilane.

Specific examples thereof include polycondensates obtained by hydrolysisand polycondensation of the compounds represented by the general formula(II) and/or (iii) and/or oligomers thereof.

M^(m+)X_(n)Y¹ _(m-n)  (ii)

In the formula (II), M represents at least one element selected fromsilicon, aluminum, zirconium, and titanium. X represents a hydrolyzablegroup. Y¹ represents a monovalent organic group. m represents thevalence of M and an integer of 1 or more, and n represents the number ofX groups and an integer of 1 or more, provided that m≧n.

M^(s+)X_(t)Y¹ _(s-t-1)  (iii)

In the formula (iii), M represents at least one element selected fromsilicon, aluminum, zirconium, and titanium. X represents a hydrolyzablegroup. Y¹ represents a monovalent organic group. Y² represents u-valentorganic group. s represents the valence of M and an integer of 1 ormore, t represents an integer of 1 to s−1, and u represents an integerof 2 or more.

The condensation-type silicone materials may contain curing catalysts.Preferred examples of curing catalysts that can be used include metalchelate compounds. Preferably, metal chelate compounds contain any oneor more of Ti, Ta, and Zr. Particularly preferably, metal chelatecompounds contain Zr. These curing catalysts may be used alone or in anycombination of two or more in any proportion.

As the condensation-type silicone materials, members for semiconductorlight-emitting devices described in Japanese Patent Application Nos.2006-47274 to 47277 and Japanese Patent Application No. 2006-176468 arepreferred.

Among the condensation-type silicone materials, particularly preferablematerials will be described below. In general, silicone materialsdisadvantageously have low adhesion to semiconductor light-emittingelements substrates on which semiconductor light-emitting elements aremounted, and packages. With respect to silicone materials having highadhesion, in particular, condensation-type silicone materials eachhaving one or more of features [1] to [3] described below are preferred.

[1] The silicon content is 20% by weight or more.

[2] In a solid-state Si nuclear magnetic resonance (NMR) spectrummeasured by a method detailed below, at least one peak defined by items(a) and/or item (b) attributed to Si is present:

(a) a peak with a peak top that is located in the chemical shift rangeof −40 ppm to 0 ppm and with a full width at half maximum of 0.3 ppm to3.0 ppm using tetramethoxysilane as a standard; and

(b) a peak with a peak top that is located in the chemical shift rangefrom −80 ppm to less than −40 ppm and with a full width at half maximumof 0.3 ppm to 5.0 ppm using tetramethoxysilane as a standard.

[3] The silanol content is 0.1% by weight to 10% by weight.

In the present invention, the silicone materials each having feature [1]among features [1] to [3] are preferred. The silicone materials eachhaving features [1] and [2] are more preferred. The silicone materialseach having all features [1] to [3] are particularly preferred.

Features [1] to [3] will be described below.

<Feature [1] (Silicon Content)>

The basic skeleton of a known silicone material is of carbon-carbon andcarbon-oxygen bonds, and such a silicone material is an organic resinsuch as an epoxy resin. In contrast, the basic skeleton of the siliconematerial used in the present invention is of inorganic siloxane bondsand is the same as that of glass (silicate glass). As is clear fromTable 1, which is a chemical-bond comparison table, the siloxane bondhas excellent characteristics described below as a silicone material.

(I) The bond energy of the siloxane bond is large; hence, the siloxanebond is not easily decomposed by heat or light, leading to satisfactorylight resistance.

(II) The siloxane bond is slightly electrically polarized.

(III) The chain structure having a high degree of freedom makes itpossible to form a structure with good flexibility. The structure canfreely rotate around the siloxane chain.

(IV) The siloxane bond has a high degree of oxidation and thus is notfurther oxidized.

(V) The siloxane bond has satisfactory electrical insulating properties.

TABLE 1 Chemical-bond comparison table Bond distance Bond energy Bondangle Bond (Å) (kcal/mol) (°) Si—C—Si 1.64 108 130~160 C—O—C 1.43  86110 C—C—C 1.54  85 109

It is understood from these characteristics that a silicone materialcomposed of a silicone having a skeleton in which siloxane bonds arethree-dimensionally formed with a high degree of crosslinking behaveslike an inorganic material, such as glass or rock, and that a protectivefilm composed of such a silicone material has satisfactory heatresistance and light resistance. In particular, a silicone materialhaving a methyl group as a substituent does not have absorption in theultraviolet region and thus does not easily decomposed by light.Thereby, such a silicone material has excellent light resistance.

The silicon content of the silicone material suitably used in thepresent invention is usually 20% by weight or more, preferably 25% byweight or more, and more preferably 30% by weight or more. The upperlimit is usually 47% by weight or less because glass that consists ofSiO₂ has a silicon content of 47% by weight.

The silicon content of the silicone material can be calculated on thebasis of results obtained by inductively coupled plasma spectrometry(hereinafter, appropriately abbreviated as “ICP”) using, for example,the following method.

[Measurement of Silicon Content]

A silicone material is baked at 450° C. for 1 hour, 750° C. for 1 hour,and 950° C. for 1.5 hours in a platinum crucible in air to remove carboncomponents. Then, sodium carbonate is added to a small portion of theresulting residue in an amount of 10 or more times the amount of theportion of the residue. The mixture is heated with a burner to melt themixture and then cooled. Desalted water is added thereto. The resultingsolution is diluted to a specific volume in such a manner that theconcentration of silicon is about several ppm while the pH is adjustedto approximately neutral with hydrochloric acid. Then ICP analysis isperformed.

<Feature [2] (Solid-State Si-NMR Spectrum)>

Measurement of the solid-state Si-NMR spectrum of the silicone materialsuitable for the present invention demonstrates that at least one peakand preferably a plurality of peaks are observed in the region definedby item (a) and/or item (b) attributed to silicon atoms directly bondedto carbon atoms of organic groups.

The full widths at half maximum are organized by chemical shifts asfollows. In the silicone material suitable for the present invention,the full width at half maximum of the peak described in item (a) isgenerally smaller than that of the peak described in item (b) because ofmoderate restriction of molecular motion, and is usually 3.0 ppm or lessand preferably 2.0 ppm or less, and usually 0.3 ppm or more.

Meanwhile, the full width at half maximum of the peak described in item(b) is usually 5.0 ppm or less and preferably 4.0 ppm or less, andusually 0.3 ppm or more and preferably 0.4 ppm or more.

An excessively large full width at half maximum of the peak observed ineach of the chemical shift regions described above means an increase instrain due to severe restriction of molecular motion, thereby may causeeasily forming cracks and possibly resulting in a member having poorheat resistance, weather resistance, and durability. Examples of thecase where the range of the full width at half maximum is larger thanthe range described above are as follows: for example, the case in whicha large amount of a tetrafunctional silane is used; and the case inwhich rapid drying in a drying step results in the accumulation ofincreased internal stress.

In the case where the full width at half maximum of the peak isexcessively small, Si atoms present in such an environment do notparticipate in siloxane crosslinking. For example, the presence of atrifunctional silane remaining in an uncrosslinked state may result in amember having poor heat resistance, weather resistance, and durabilitycompared with those of a material mainly having siloxane bonds.

However, even if a peak of a silicone material containing a small amountof a Si component in a large amount of an organic component has a fullwidth at half maximum within the above range at −80 ppm or more,satisfactory heat resistance, light resistance, and applicationperformance cannot be obtained, in some cases.

The value of the chemical shift of the silicone material suitable forthe present invention can be calculated on the basis of results obtainedby performing solid-state Si-NMR measurement according to the followingmethod. Analysis of measurement data (analysis of the full width at halfmaximum and the amount of silanol) is performed by a method in whichpeaks are separated and extracted by waveform separation analysis using,for example, the Gaussian function and the Lorenz function.

[Solid-State Si-NMR Spectrum Measurement and Calculation of SilanolContent]

In the case where solid-state Si-NMR spectrum measurement of a siliconematerial is performed, solid-state Si-NMR spectrum measurement andwaveform separation analysis are performed under conditions describedbelow. The full width at half maximum of each of the peaks of thesilicone material is determined on the basis of the resulting waveformdata. The proportion M of silicon atoms of silanol to the total siliconatoms is determined on the basis of the ratio of a peak area resultingfrom silanol to the total peak area. In comparison to a silicon contentseparately analyzed, the silanol content is determined.

{System Conditions}

System: Infinity CMX-400 nuclear magnetic resonance spectrometer,manufactured by Chemagnetics Inc.

²⁹Si resonance frequency: 79.436 MHz

Probe: CP/MAS probe with a diameter of 7.5 mm

Temperature during measurement: Room temperature

Number of rotation of sample: 4 kHz

Method for measurement: Single-pulse method

¹H decoupling frequency: 50 kHz

²⁹Si flip angle: 90°

²⁹Si 90° pulse duration: 5.0 μs

Repetition time: 600 s

Number of accumulations: 128

Observation range: 30 kHz

Broadening factor: 20 Hz

Standard sample: Tetramethoxysilane

For a silicone material, 512 points are recorded as measurement data andzero-filled to 8192 points prior to Fourier transformation.

[Waveform Separation Analysis]

For each of the peaks in the spectrum after Fourier transformation, apeak shape is formed using a Lorentz waveform, a Gaussian waveform, or amixture of both. Optimization calculation is performed by a nonlinearleast-squares method using the center position, height, and full widthat half maximum of the peak shape as variable parameters.

The peaks are identified with reference to, for example, AIChE Journal,44(5), p. 1141, 1998.

<Feature [3] (Silanol Content)>

The silicone material suitable for the present invention has a silanolcontent of usually 0.1% by weight or more and preferably 0.3% by weightor more, and usually 10% by weight or less, preferably 8% by weight orless, and more preferably 5% by weight or less. The silicone materialhas a low silanol content and thus excellent performance, i.e., only asmall change with time, excellent long-term performance stability, lowhygroscopicity, and low moisture permeability. However, a member thatdoes not contain silanol at all has poor adhesion. Therefore, theabove-described optimum range of the silanol content is set.

The silanol content of a silicone material can be determined as follows:Solid-state Si-NMR spectrum measurement is performed by the methoddescribed in “(Solid-State Si-NMR Spectrum Measurement and Calculationof Silanol content)” in “<Feature [2] (Solid-State Si-NMR Spectrum)”.The proportion (%) of silicon atoms of silanol to the total siliconatoms is determined on the basis of the ratio of a peak area resultingfrom silanol to the total peak area. In comparison to a silicon contentseparately analyzed, the silanol content is calculated.

The silicone material suitable for the present invention contains anappropriate amount of silanol. Thus, silanol is usually hydrogen-bondedto a polar portion present on a surface of a device, resulting inadhesion. Examples of the polar portion include hydroxy groups andoxygen of metalloxane bonds.

Usually, the silicone material suitable for the present invention isheated in the presence of a proper catalyst to form covalent bonding tothe hydroxy groups on a surface of a device by dehydration condensation,thereby resulting in stronger adhesion.

An excessively large amount of silanol may increase the viscosity of thesystem, which makes application more difficult. Furthermore, anexcessively large amount of silanol may increase activity to cause thesolidification by heat before low-boiling-point components volatilize,resulting in foaming and an increase in internal stress. This may inducecracking.

<Liquid Medium Content>

The liquid medium content of the phosphor-containing composition of thepresent invention is not limited unless the content significantlyimpairs the advantage of the present invention. The liquid mediumcontent is usually 50% by weight or more and preferably 75% by weight ormore, and usually 99% by weight or less and preferably 95% by weight orless with respect to the total amount of the phosphor-containingcomposition of the present invention. When a large amount of the liquidmedium is used, there is no particular problem. To obtain alight-emitting device having target chromaticity coordinates, anintended color rendering index, desired luminous efficiency, and thelike, usually, the liquid medium is preferably used in the mixing ratiodescribed above. An excessively low liquid medium content may eliminateflowability, making the handling difficult.

The liquid medium serves mainly as a binder in the phosphor-containingcomposition of the present invention. The liquid medium may be usedalone or in combination of two or more in any proportion. For example,in the case where a silicon-containing compound is used to achieve goodheat resistance and light resistance, the liquid medium may contain anadditional thermosetting resin such as an epoxy resin to the extent thatthe durability of the silicon-containing compound is not impaired. Inthis case, the additional thermosetting resin content is usually 25% byweight or less and preferably 10% by weight or less with respect to thetotal amount of the liquid medium serving as a binder.

<Additional Component>

The phosphor-containing composition of the present invention may furthercontain additional components in addition to the phosphor and the liquidmedium unless they significantly impair the advantage of the presentinvention. The additional components may be used alone or in combinationof two or more in any proportion.

<Advantage of Phosphor-Containing Composition>

According to the phosphor-containing composition of the presentinvention, the phosphor of the present invention can be easily fixed atan intended position. For example, in the case where thephosphor-containing composition of the present invention is used forproducing a light-emitting device, the phosphor-containing compositionof the present invention is shaped at an intended position. Curing theliquid medium seals the phosphor of the present invention with theliquid medium, thereby making it possible to easily fix the phosphor ofthe present invention at an intended position.

{Light-Emitting Device}

A light-emitting device of the present invention will be describedbelow.

The light-emitting device of the present invention (hereinafter,appropriately referred to as a “light-emitting device”) indicates afirst illuminant (excitation light source) and a second illuminant thatemits visible light by irradiation with light emitted from the firstilluminant. The second illuminant contains one or two or more of thephosphors of the present invention as a first phosphor.

The composition and the emission color of the phosphor of the presentinvention used for the light-emitting device of the present inventionare not particularly limited as long as the phosphor is the phosphor ofthe present invention. For example, in the case where the phosphor ofthe present invention is represented by the general formula [2] andcontains Eu serving as the activating element M¹, the phosphor of thepresent invention is usually a phosphor that emits orange to redfluorescence (hereinafter, also referred to as an “orange to redphosphor of the present invention”) under irradiation with light from anexcitation source. Specifically, in the case where the phosphor of thepresent invention is an orange to red phosphor of the present invention,the phosphor preferably has an emission peak in the wavelength range of590 nm to 640 nm. The phosphor of the present invention may be usedalone. Alternatively, any two or more of the phosphors may be combinedin any proportion.

The weight-average median diameter D₅₀ of the phosphor of the presentinvention used for the light-emitting device of the present invention isusually 10 μm or more and preferably 15 μm or more, and usually 30 μm orless and preferably 20 μm or less. An excessively small weight-averagemedian diameter D₅₀ is liable to cause a reduction in brightness andlead to aggregation of the phosphor particles. An excessively largeweight-average median diameter D₅₀ is liable to cause an uneven coatingand clogging of a dispenser or the like.

Preferred examples of the phosphor of the present invention used for thelight-emitting device of the present invention include the phosphors ofthe present invention described in “{Composition of Phosphor}” above;and phosphors used in examples described in “[EXAMPLES]” below.

The structure of the light-emitting device of the present invention isnot limited as long as the light-emitting device has the firstilluminant (excitation light source) and the phosphor of the presentinvention as the second illuminant. The light-emitting device of thepresent invention may have any known device structure. Specific examplesof the device structure will be described below.

The emission peak observed in an orange to red region in an emissionspectrum of the light-emitting device of the present invention ispreferably present in the wavelength of 590 nm to 670 nm.

In particular, a white-light-emitting device, having a known devicestructure, according to the light-emitting device of the presentinvention includes an excitation light source described below serving asthe first illuminant; and any combination of phosphors, for example, anorange to red phosphor as described above, a known phosphor that emitsgreen fluorescence (hereinafter, appropriately referred to as a “greenphosphor”), a known phosphor that emits blue fluorescence (hereinafter,appropriately referred to as a “blue phosphor”), a known phosphor thatemits yellow fluorescence (hereinafter, appropriately referred to as a“yellow phosphor”), and the like, as described below.

The term “white” defined herein includes (yellowish) white, (greenish)white, (bluish) white, (purplish) white, and white specified by JISZ8701 and preferably means white.

<Structure of Light-Emitting Device (Illuminant)> [First Illuminant]

The first illuminant in the light-emitting device of the presentinvention emits light to excite the second illuminant described below.

The emission wavelengths of the first illuminant are not particularlylimited as long as the emission wavelengths overlap the absorptionwavelengths of the second illuminant described below. An illuminanthaving a wide emission wavelength range can be used. Usually, anilluminant having emission wavelengths from the ultraviolet region tothe blue region is used. Particularly preferably, an illuminant havingemission wavelengths from the near-ultraviolet region to the blue regionis used.

With respect to the specific value of the peak emission wavelength ofthe first illuminant, the first illuminant preferably has a peakemission wavelength of 200 nm or more. In the case of usingnear-ultraviolet light serving as excitation light, it is preferable touse the illuminant having a peak emission wavelength of usually 300 nmor more, preferably 330 nm or more, and more preferably 360 nm or more,and usually 420 nm or less. In the case of using blue light serving asexcitation light, it is preferable to use the illuminant having a peakemission wavelength of usually 420 nm or more, preferably 430 nm ormore, and usually 500 nm or less and preferably 480 nm or less. Thereason for these ranges is that good color purity of theselight-emitting devices is achieved.

As the first illuminant, a semiconductor light-emitting element isgenerally used. Specifically, for example, light-emitting diodes andsemiconductor laser diodes (hereinafter, appropriately referred to as“LDs”) can be used. Other examples of the illuminant that can be used asthe first illuminant include organic electroluminescent light-emittingelements and inorganic electroluminescent light-emitting elements.However, the illuminant that can be used as the first illuminant is notlimited to illuminants exemplified in this specification.

Among these, as the first illuminant, GaN-based LEDs and LDs includingGaN-based compound semiconductors are preferred. This is becauseGaN-based LEDs and LDs each have markedly large emission power andexternal quantum efficiency compared with those of SiC-based LEDs andthe like emitting light in this region, and a combination of eitherGaN-based LED or LD and the phosphor of the present invention results invery bright emission at ultra-low power. For example, when a currentload is 20 mA, usually, GaN-LEDs and LDs each have light emissionintensity 100 or more times higher than SiC-based LEDs and the like.GaN-LEDs and LDs each including an Al_(X)Ga_(Y)N emission layer, a GaNemission layer, or an In_(X)Ga_(Y)N emission layer are preferred. InGaN-based LEDs, among these, GaN-based LEDs each including anIn_(X)Ga_(Y)N emission layer are particularly preferred because of veryhigh light emission intensity. In GaN-based LEDs, GaN-based LEDs eachhaving a multiple-quantum-well structure including an In_(X)Ga_(Y)Nlayer and a GaN layer are particularly preferred because of very highlight emission intensity.

The value of X+Y is usually in the range of 0.8 to 1.2. In GaN-basedLEDs, a doped emission layer obtained by doping the emission layer withZn or Si and an undoped emission layer are preferred to adjust emissionproperties.

GaN-based LEDs each includes the emission layer, a p layer, an n layer,electrodes, and a substrate, as fundamental constituents. GaN-based LEDseach having a heterostructure in which the emission layer is arrangedbetween, for example, n- and p-type Al_(X)Ga_(Y)N layers, GaN layers, orIn_(X)Ga_(Y)N layers are preferred because of high luminous efficiency.Furthermore, GaN-based LEDs each having a structure in which theheterostructure is a multiple-quantum-well structure are more preferredbecause of further high luminous efficiency. The first illuminant may beused alone. Alternatively, any two or more of the first illuminants maybe combined in any proportion.

[Second Illuminant]

The second illuminant in the light-emitting device of the presentinvention is an illuminant that emits visible light by irradiation withlight emitted from the first illuminant. The second illuminant containsthe phosphor of the present invention (e.g., the orange to red phosphor)as the first phosphor and optionally contains a second phosphor (e.g., agreen phosphor, a blue phosphor, or a yellow phosphor) described belowaccording to an application and the like. For example, the secondilluminant includes the first and second phosphors dispersed in asealing material.

Compositions of the phosphors, used in the second illuminant, other thanthe phosphor of the present invention are not particularly limited.Examples of the phosphors include compounds having metal oxides, such asY₂O₃, YVO₄, Zn₂SiO₄, Y₃Al₅O₁₂, and Sr₂SiO₄, metal nitrides such asSr₂Si₅N₈, phosphates such as Ca₅(PO₄)₃Cl, sulfides, such as ZnS, SrS,CaS, and oxysulfides, such as Y₂O₂S, and La₂O₂S, which serve ascrystalline matrices, in combination with ions of rare-earth metals,such as Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb and ions ofmetals, such as Ag, Cu, Au, Al, Mn, and Sb, which serve as activatingelement or co-activating elements.

Preferred examples of the crystalline matrices include sulfides, such as(Zn,Cd)S, SrGa₂S₄, SrS, and ZnS; oxysulfides such as Y₂O₂S; aluminates,such as (Y,Gd)₃Al₅O₁₂, YAlO₃, BaMgAl₁₀O₁₇, (Ba,Sr)(Mg,Mn)Al₁₀O₁₇,(Ba,Sr,Ca)(Mg,Zn,Mn) Al₁₀O₁₇, BaAl₁₂O₁₉, CeMgAl₁₁O₁₉, (Ba,Sr,Mg)O.Al₂O₃,BaAl₂Si₂O₈, SrAl₂O₄, Sr₄Al₁₄O₂₅, and Y₃Al₅O₁₂; silicates, such as Y₂SiO₅and Zn₂SiO₄; oxides such as SnO₂ and Y₂O₃; borates, such as GdMgB₅O₁₀and (Y,Gd)BO₃; halophosphates, such as Ca₁₀(PO₄)₆(F,Cl)₂ and(Sr,Ca,Ba,Mg)₁₀(PO₄)₆Cl₂; and phosphates, such as Sr₂P₂O₇ and(La,Ce)PO₄.

With respect to the crystalline matrices and the activation elements orthe co-activating elements, elemental compositions are not particularlylimited. The elements in the compositions may be partially replaced withan element in the same group. When the resulting phosphor absorbs lightin the near-ultraviolet to visible regions to emit visible light, thephosphor may be used.

Specifically, the following phosphors may be used. These are onlyexamples. Phosphors that can be used in the present invention are notlimited thereto.

In the following examples, phosphors in which the difference between thephosphors is only part of their structures are described withappropriate omissions as described above.

[First Phosphor]

The second illuminant in the light-emitting device of the presentinvention contains at least the phosphor of the present inventiondescribed above as the first phosphor. The phosphors of the presentinvention may be used alone. Alternatively, any two or more of thephosphors of the present invention may be combined in any proportion.Furthermore, as the first phosphor, a phosphor that emits fluorescenceof the same color as that of the phosphor of the present invention(same-color combination phosphor) may be used in addition to thephosphor of the present invention. For example, in the case where thephosphor of the present invention is represented by the general formula[2] and contains Eu serving as the activating element M¹, the phosphorof the present invention is usually an orange to red phosphor. Thus, anorange to red phosphor other than the phosphor of the present inventionserving as the first phosphor can be combined with the phosphor of thepresent invention.

Any orange to red phosphor may be used unless the advantage of thepresent invention is significantly impaired.

The peak emission wavelength of the orange to red phosphor serving asthe same-color combination phosphor is usually 570 nm or more,preferably 580 nm or more, and more preferably 585 nm or more, andusually 780 nm or less, preferably 700 nm or less, and more preferably680 nm or less.

Examples of such a orange to red phosphor include europium-activatedalkaline-earth silicon nitride phosphors constituted by fracturedparticles having red fracture surfaces, emitting light in the redregion, and represented by (Mg,Ca,Sr,Ba)₂Si₅N₈:Eu; andeuropium-activated rare-earth oxychalcogenide phosphors constituted bygrown particles each having a substantially spherical shape as a regularcrystal growth shape, emitting light in the red region, and representedby (Y,La,Gd,Lu)₂O₂S:Eu.

Phosphors, described in Japanese Unexamined Patent ApplicationPublication No. 2004-300247, each containing oxynitride and/oroxysulfide containing at least one element selected from the groupconsisting of Ti, Zr, Hf, Nb, Ta, W, and Mo, and each containing theoxynitride having an α-SiAlON structure in which the whole or part of Alelement is replaced with Ga element, can also be used in the presentinvention. These are phosphors each containing oxynitride and/oroxysulfide.

Other examples of the red phosphor that can be used include Eu-activatedoxysulfide phosphors such as (La,Y)₂O₂S:Eu; Eu-activated oxide phosphorssuch as Y(V,P)O₄:Eu and Y₂O₃:Eu; Eu, Mn-activated silicate phosphors,such as (Ba,Mg)₂SiO₄:Eu,Mn and (Ba,Sr,Ca,Mg)₂SiO₄:Eu,Mn; Eu-activatedtungstate phosphors, such as LiW₂O₈:Eu, LiW₂O₈:Eu,Sm, Eu₂W₂O₉,Eu₂W₂O₉:Nb, and Eu₂W₂O₉:Sm; Eu-activated sulfide phosphors such as(Ca,Sr)S:Eu; Eu-activated aluminate phosphors such as YAlO₃:Eu;Eu-activated silicate phosphors, such as Ca₂Y₈ (SiO₄)₆O₂:Eu,LiY₉(SiO₄)₆O₂:Eu, (Sr,Ba,Ca)₃SiO₈:Eu, and Sr₂BaSiO₈:Eu; Ce-activatedaluminate phosphors, such as (Y,Gd)₃Al₈O₁₂:Ce and (Tb,Gd)₃Al₅O₁₂:Ce;Eu-activated oxide, nitride, or oxynitride phosphors such as(Mg,Ca,Sr,Ba)₂Si₈(N,O)₈:Eu, (Mg,Ca,Sr,Ba)Si(N,O)₂:Eu, and(Mg,Ca,Sr,Ba)AlSi(N,O)₃:Eu; Ce-activated oxide, nitride, or oxynitridephosphors such as (Mg,Ca,Sr,Ba)AlSi(N,O)₃:Ce; Eu,Mn-activatedhalophosphate phosphors such as (Sr,Ca,Ba,Mg)₁₀(PO₄)₈Cl₂:Eu,Mn;Eu,Mn-activated silicate phosphors such as Ba₃MgSi₂O₈:Eu,Mn and(Ba,Sr,Ca,Mg)₃(Zn,Mg)Si₂O₈:Eu,Mn; Mn-activated germanate phosphors suchas 3.5MgO0.5MgF₂.GeO₂:Mn; Eu-activated oxynitride phosphors such asEu-activated α-SiAlON; Eu,Bi-activated oxide phosphors such as(Gd,Y,Lu,La)₂O₃:Eu,Bi; Eu,Bi-activated oxysulfide phosphors such as(Gd,Y,Lu,La)₂O₂S:Eu,Bi; Eu,Bi-activated vanadate phosphors such as(Gd,Y,Lu,La)VO₄:Eu,Bi; Eu,Ce-activated sulfide phosphors such asSrY₂S₄:Eu,Ce; Ce-activated sulfide phosphors such as CaLa₂S₄:Ce;Eu,Mn-activated phosphate phosphors such as (Ba,Sr,Ca)MgP₂O₇:Eu,Mn and(Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu,Mn; Eu,Mo-activated tungstate phosphors such as(Y,Lu)₂WO₆:Eu,Mo; Eu,Ce-activated nitride phosphors such as(Ba,Sr,Ca)_(x)Si_(y)N_(z):Eu,Ce (wherein x, y, and z each represent aninteger of one or more); Eu,Mn-activated halophosphate phosphors such as(Ca,Sr,Ba,Mg)₁₀(PO₄)₆(F,Cl,Br,OH)₂:Eu,Mn; and Ce-activated silicatephosphors such as ((Y,Lu,Gd,Tb)_(1-z-y)Sc_(x)Ce_(y))₂(Ca,Mg)_(1-r)(Mg/Zn)_(2+r)Si_(z-q)Ge_(q)O_(12+δ).

Examples of the red phosphor that can be used include red organicphosphors each composed of a rare-earth element ion complex having ananionic ligand, e.g., a β-diketonate, a β-diketone, an aromaticcarboxylic acid, or a Broensted acid; perylene pigments (e.g.,dibenzo{[f,f′]-4,4′,7,7′-tetraphenyl}diindeno[1,2,3-cd:1′,2′,3′-lm]perylene);anthraquinone pigments; lake pigments; azo pigments; quinacridonepigments; anthracene pigments; isoindoline pigments; isoindolinonepigments; phthalocyanine pigments; triphenylmethane basic dyes;indanthrone pigments; indophenol pigments; cyanin pigments; anddioxazine pigments.

Among these, the red phosphor preferably contains(Ca,Sr,Ba)₂Si₅(N,O)₈:Eu, (Ca,Sr,Ba)Si(N,O)₂:Eu, (Ca,Sr,Ba)AlSi(N,O)₃:Eu,(Ca,Sr,Ba)AlSi(N,O)₃:Ce, (Sr,Ba)₃SiO₈:Eu, (Ca,Sr)S:Eu, (La,Y)₂O₂S:Eu, ora Eu complex. More preferably, the red phosphor contains(Ca,Sr,Ba)₂Si₅(N,O)₈:Eu, (Ca,Sr,Ba)Si(N,O)₂Eu, (Ca,Sr,Ba)AlSi(N,O)₃:Eu,(Ca,Sr,Ba)AlSi(N,O)₃:Ce, (Sr,Ba)₃SiO₅:Eu, (Ca,Sr)S:Eu, or (La,Y)₂O₂S:Eu;a β-diketone-based Eu complex such as Eu(dibenzoylmethane)₃.1,10-phenanthroline complex; or a carboxylicacid-based Eu complex. Particularly preferably, the red phosphorcontains (Ca,Sr,Ba)₂Si₅(N,O)₈:Eu, (Sr,Ca)AlSiN₃:Eu, or (La,Y)₂O₂S:Eu.

Among these examples, (Sr,Ba)₃SiO₅:Eu is preferably used as an orangephosphor.

These exemplified orange to red phosphors may be used alone or incombination of two or more in any proportion.

[Second Phosphor]

The second illuminant in the light-emitting device of the presentinvention may contain a phosphor (second phosphor) according to anapplication in addition to the first phosphor described above. Thesecond phosphor is a phosphor that differs in peak emission wavelengthfrom the first phosphor. Usually, the second phosphor is used to adjustthe emission color of the second illuminant. Thus, a phosphor that emitsfluorescence of color different from that of the first phosphor is oftenused as the second phosphor. In the case where the orange to redphosphor is used as the first phosphor as described above, a phosphor,e.g., a green phosphor, a blue phosphor, or a yellow phosphor, thatemits light of color different from that of the first phosphor is usedas the second phosphor.

The weight-average median diameter D₅₀ of the second phosphor is usually10 μm or more and preferably 12 μm or more, and usually 30 μm or lessand preferably 25 μm or less. An excessively small weight-average mediandiameter D₅₀ is liable to cause a reduction in brightness and lead toaggregation of the phosphor particles. An excessively largeweight-average median diameter D₅₀ is liable to cause an uneven coatingand clogging of a dispenser or the like.

<Blue Phosphor>

In the case where a blue phosphor is used as the second phosphor, anyblue phosphor can be used unless the blue phosphor significantly impairsthe advantage of the present invention. In this case, the peak emissionwavelength of the blue phosphor is usually 420 nm or more, preferably430 nm or more, and more preferably 440 nm or more, and usually 490 nmor less, preferably 480 nm or less, more preferably 470 nm or less, andstill more preferably 460 nm or less.

Examples of the blue phosphor include europium-activated bariummagnesium aluminate phosphors constituted by grown particles each havinga substantially hexagonal shape as a regular crystal growth shape,emitting light in the blue region, and represented by(Ba,Sr,Ca)MgAl₁₀O₁₇:Eu; europium-activated calcium halophosphatephosphors constituted by grown particles each having a substantiallyspherical shape as a regular crystal growth shape, emitting light in theblue region, and represented by (Mg,Ca,Sr,Ba)₅(PO₄)₃(Cl,F):Eu;europium-activated alkaline-earth chloroborate phosphors constituted bygrown particles each having a substantially cubic shape as a regularcrystal growth shape, emitting light in the blue region, and representedby (Ca,Sr,Ba)₂B₅O₉Cl:Eu; and europium-activated alkaline-earth aluminatephosphors constituted by fractured particles having fracture surfaces,emitting light in the blue-green region, and represented by(Sr,Ca,Ba)Al₂O₄:Eu or (Sr,Ca,Ba)₄Al₁₄O₂₅:Eu.

Other examples of the blue phosphor include Sn-activated phosphatephosphors such as Sr₂P₂O₇:Sn; Eu-activated aluminate phosphors such as(Sr,Ca,Ba)Al₂O₄:Eu, (Sr,Ca,Ba)₄Al₁₄O₂₅:Eu, BaMgAl₁₀O₁₇:Eu,(Ba,Sr,Ca)MgAl₁₀O₁₇:Eu, BaMgAl₁₀O₁₇:Eu,Tb,Sm, and BaAl₈O₁₃:Eu;Ce-activated thiogallate phosphors such as SrGa₂S₄:Ce and CaGa₂S₄:Ce;Eu,Mn-activated aluminate phosphors such as (Ba,Sr,Ca)MgAl₁₀O₁₇:Eu,Mn;Eu-activated halophosphate phosphors such as (Sr,Ca,Ba,Mg)₁₀(PO₄)₆Cl₂:Euand (Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu,Mn,Sb; Eu-activated silicatephosphors such as BaAl₂Si₂O₈:Eu and (Sr,Ba)₃MgSi₂O₈:Eu; Eu-activatedphosphate phosphors such as Sr₂P₂O₇:Eu; sulfide phosphors such as ZnS:Agand ZnS:Ag,Al; Ce-activated silicate phosphors such as Y₂SiO₅:Ce;tungstate phosphors such as CaWO₄; Eu,Mn-activated borate phosphatephosphors, such as (Ba,Sr,Ca)BPO₅:Eu,Mn, (Sr,Ca)₁₀(PO₄)₆.nB₂O₃:Eu, and2SrO.0.84P₂O₅.0.16B₂O₃:Eu; Eu-activated halosilicate phosphors such asSr₂Si₃O₈.2SrCl₂:Eu; Eu-activated oxynitride phosphors, such asSrSi₉Al₁₉ON₃₁:Eu and EuSi₉Al₁₉ON₃₁; and Ce-activated oxynitridephosphors, such as La_(1-x)Ce_(x)Al(Si_(6-z)Al_(z)) (N_(10-z)O_(z))(wherein x and y represent values satisfying 0≦x≦1 and 0≦z≦6,respectively) and La_(1-x-y)Ce_(x)Ca_(y)Al(Si_(6-z)Al_(z))(N_(10-z)O_(z)) (wherein x, y, and z represent values satisfying 0≦x≦1,0≦y≦1, and 0≦z≦6, respectively).

Furthermore, examples of the blue phosphor that can be used includefluorescent dyes such as naphthalic imide, benzoxazole, styryl,coumarin, pyrazoline, and triazole compounds; and organic phosphors suchas thulium complexes and the like.

Among these examples, the blue phosphor preferably contains(Ca,Sr,Ba)MgAl₁₀O₁₇:Eu, (Sr,Ca,Ba,Mg)₁₀(PO₄)₆(Cl,F)₂:Eu, or(Ba,Ca,Mg,Sr)₂SiO₄:Eu. More preferably, the blue phosphor contains(Ca,Sr,Ba)MgAl₁₀O₁₇:Eu, (Sr,Ca,Ba,Mg)₁₀(PO₄)₆(Cl,F)₂:Eu, or(Ba,Ca,Sr)₃MgSi₂O₈:Eu. Still more preferably, the blue phosphor containsBaMgAl₁₀O₁₇:Eu, Sr₁₀(PO₄)₆(Cl,F)₂:Eu, or Ba₃MgSi₂O₈:Eu.(Sr,Ca,Ba,Mg)₁₀(PO₄)₆Cl₂:Eu or (Ca,Sr,Ba)MgAl₁₀O₁₇:Eu is particularlypreferred for illumination and display application.

These exemplified blue phosphors may be used alone or in combination oftwo or more in any proportion.

<Yellow Phosphor>

In the case where a yellow phosphor is used as the second phosphor, anyyellow phosphor can be used unless the yellow phosphor significantlyimpairs the advantage of the present invention. In this case, the peakemission wavelength of the yellow phosphor is usually 530 nm or more,preferably 540 nm or more, and more preferably 550 nm or more, andusually 620 nm or less, preferably 600 nm or less, and more preferably580 nm or less.

Examples of the yellow phosphor include phosphors of various oxides,nitrides, oxynitrides, sulfides, and oxysulfides.

Specific examples thereof include Ce-activated phosphors, for example,garnet phosphors having a garnet structure, such as RE₃M₅O₁₂:Ce (whereinRE represents at least one element selected from the group consisting ofY, Tb, Gd, Lu, and Sm; and M represents at least one element selectedfrom the group consisting of Al, Ga, and Sc) and M^(a) ₃M^(b) ₂M^(c)₃O₁₂:Ce (wherein M^(a) represents a divalent metal element; M^(b)represents a trivalent metal element; and M^(c) represents a tetravalentmetal element), orthosilicate phosphors such as AE₂M^(d)O₄:Eu (whereinAE represents at least one element selected from the group consisting ofBa, Sr, Ca, Mg, and Zn; and M^(d) represents Si and/or Ge), oxynitridephosphors in which oxygen as a constituent of these phosphors ispartially replaced with nitrogen, and nitride phosphors having aCaAlSiN₃ structure, such as AEAlSiN₃:Ce (wherein AE represents at leastone element selected from the group consisting of Ba, Sr, Ca, Mg, andZn).

Other examples of the yellow phosphor that can be used includeEu-activated phosphors, such as sulfide phosphors, e.g., CaGa₂S₄:Eu,(Ca,Sr)Ga₂S₄:Eu, and (Ca,Sr)(Ga,Al)₂S₄:Eu, and oxynitride phosphorshaving a SiAlON structure, e.g., Cax(Si,Al)₁₂(O,N)₁₆:Eu; andEu-activated or Eu,Mn-coactivated halogenated borate phosphors such as(M_(1-A-A)Eu_(A)Mn_(A))₂(BO₃)_(1-P)(PO₄)_(P)X (wherein M represents atleast one element selected from the group consisting of Ca, Sr, and Ba;X represents at least one element selected from the group consisting ofF, Cl, and Br; A, B, and P represent values satisfying 0.001≦A≦0.3,0≦B≦0.3, and 0≦P≦0.2, respectively).

Other examples of the yellow phosphor that can be used includefluorescent dyes, such as brilliant sulfoflavine FF (colour index number56205), basic yellow HG (colour index number 46040), eosine (colourindex number 45380), and rhodamine 6G (colour index number 45160).

These exemplified yellow phosphors may be used alone or in combinationof two or more in any proportion.

<Green Phosphor>

In the case where a green phosphor is used as the second phosphor, anygreen phosphor can be used unless the green phosphor significantlyimpairs the advantage of the present invention. In this case, the peakemission wavelength of the green phosphor is usually 500 nm or more,preferably 510 nm or more, and more preferably 515 nm or more, andusually 550 nm or less, preferably 542 nm or less, and more preferably535 nm or less. An excessively short peak emission wavelength is liableto lead to bluish light. An excessively long peak emission wavelength isliable to lead to yellowish light. In both cases, the phosphor can emitlight with reduced properties as green light.

Specific examples of the green phosphor include europium-activatedalkaline-earth silicon oxynitride phosphors constituted by fracturedparticles having fracture surfaces, emitting light in the green region,and represented by (Mg,Ca,Sr,Ba)Si₂O₂N₂:Eu.

Other examples of the green phosphor that can be used includeEu-activated aluminate phosphors, such as Sr₄Al₁₄O₂₅:Eu and(Ba,Sr,Ca)Al₂O₄:Eu; Eu-activated silicate phosphors, such as(Sr,Ba)Al₂Si₂O₅:Eu, (Ba,Mg)₂SiO₄:Eu, (Ba,Sr,Ca,Mg)₂SiO₄:Eu,(Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu, and(Ba,Ca,Sr,Mg)₉(Sc,Y,Lu,Gd)₂(Si,Ge)₅O₂₄:Eu; Ce,Tb-activated silicatephosphors such as Y₂SiO₅:Ce,Tb; Eu-activated borate phosphate phosphorssuch as Sr₂P₂O₇—Sr₂B₂O₅:Eu; Eu-activated halosilicate phosphors such asSr₂Si₃O₈-2SrCl₂:Eu; Mn-activated silicate phosphors such as Zn₂SiO₄:Mn;Tb-activated aluminate phosphors such as CeMgAl₁₁O₁₉:Tb, Y₃Al₅O₁₂:Tb;Tb-activated silicate phosphors such as Ca₂Y₈(SiO₄)₆O₂:Tb andLa₃Ga₅SiO₁₄:Tb; Eu,Tb,Sm-activated thiogallate phosphors such as(Sr,Ba,Ca)Ga₂S₄:Eu,Tb,Sm; Ce-activated aluminate phosphors such asY₃(Al,Ga)₅O₁₂:Ce and (Y,Ga,Tb,La,Sm,Pr,Lu)₃(Al,Ga)₅O₁₂:Ce; Ce-activatedsilicate phosphors such as Ca₃Sc₂Si₃O₁₂:Ce andCa₃(Sc,Mg,Na,Li)₂Si₃O₁₂:Ce; Ce-activated oxide phosphors such asCaSc₂O₄:Ce; Eu-activated oxynitride phosphors such as Eu-activatedβ-SiAlON; Eu,Mn-activated aluminate phosphors such as BaMgAl₁₀O₁₇:Eu,Mn;Eu-activated aluminate phosphors such as SrAl₂O₄:Eu; Tb-activatedoxysulfide phosphors such as (La,Gd,Y)₂O₂S:Tb; Ce,Tb-activated phosphatephosphors such as LaPO₄:Ce,Tb; sulfide phosphors such as ZnS:Cu,Al andZnS:Cu,Au,Al; Ce,Tb-activated borate phosphors such as(Y,Ga,Lu,Sc,La)BO₃:Ce,Tb, Na₂Gd₂B₂O₇:Ce,Tb, and(Ba,Sr)₂(Ca,Mg,Zn)B₂O₆:K,Ce,Tb; Eu,Mn-activated halosilicate phosphorssuch as Ca₈Mg(SiO₄)₄Cl₂:Eu,Mn; Eu-activated thioaluminate phosphors andthiogallte phosphors such as (Sr,Ca,Ba)(Al,Ga,In)₂S₄:Eu; Eu,Mn-activatedhalosilicate phosphors such as (Ca,Sr)₈(Mg,Zn)(SiO₄)₄Cl₂:Eu,Mn; andEu-activated oxynitride phosphors, such as M₃Si₆O₉N₄:Eu andM₃Si₆O₁₂N₂:Eu (wherein M represents an alkaline-earth metal element).

Furthermore, examples of the green phosphor that can be used includefluorescent dyes such as pyridine-phthalimide condensed derivatives,benzoxazinone, quinazolinone, coumarin, quinophthalone, and naphthalicimide; and organic phosphors such as terbium complexes and the like.

These exemplified green phosphors may be used alone or in combination oftwo or more in any proportion.

<Selection of Second Phosphor>

The second phosphor may be used alone. Alternatively, any two or more ofthe second phosphors may be combined in any proportion. The ratio of thefirst phosphor to the second phosphor is not limited unless theadvantage of the present invention is significantly impaired. Thus, forexample, the amount of the second phosphor, a combination of thephosphors used as the second phosphor, and the ratio thereof may beappropriately determined according to the application and the like ofthe light-emitting device.

In the light-emitting device of the present invention, the type ofsecond phosphor and whether or not the second phosphor (e.g., the yellowphosphor, the blue phosphor, or the green phosphor) is used may beappropriately determined according to the application of thelight-emitting device. For example, in the case where the light-emittingdevice of the present invention is used as a light-emitting device thatemits orange to red light, only the first phosphor (orange to redphosphor) may be used. In this case, usually, the second phosphor is notrequired.

In the case where the light-emitting device of the present invention isused as a white-light-emitting device, the first illuminant, the firstphosphor (orange to red phosphor), and the second phosphor may beappropriately combined in such a manner that intended white light isobtained. Specifically, preferred examples of combination of the firstilluminant, the first phosphor, and the second phosphor when thelight-emitting device of the present invention is used as awhite-light-emitting device include combinations (i) to (iii) describedbelow.

(i) A blue illuminant (e.g., a blue LED) is used as the firstilluminant, a red phosphor (e.g., the phosphor of the present invention)is used as the first phosphor, and a green phosphor is used as thesecond phosphor.

(ii) A near-ultraviolet illuminant (e.g., a near-ultraviolet LED) isused as the first illuminant, a red phosphor (e.g., the phosphor of thepresent invention) is used as the first phosphor, and a combination of ablue phosphor and a green phosphor is used as the second phosphor.

(iii) A blue illuminant (e.g., a blue LED) is used as the firstilluminant, an orange phosphor (e.g., the phosphor of the presentinvention) is used as the first phosphor, and a green phosphor is usedas the second phosphor.

Examples of the combinations of the phosphors described above will befurther described in Tables a) to h).

(Ca,Sr)AlSiNi₃:Eu exemplified as a dark-red phosphor in Tables d), h),and 5) described below is a phosphor in which the amount of Ca is 40% bymole or more with respect to the total amount of Ca and Sr and which hasa peak emission wavelength in the range of 630 nm to 700 nm. Thisphosphor may be the phosphor of the present invention.

TABLE 2 a) Orange to red light-emitting device including combination ofblue LED and orange to red phosphor of the invention Semiconductorlight- emitting element Orange to red phosphor Blue LED Orange to redphosphor of the invention b) White-light-emitting device includingcombination of blue LED, one or two or more phosphors selected fromyellow phosphors shown in Table, and orange to red phosphor of theinvention Semiconductor light- Orange to red emitting element Yellowphosphor phosphor Blue LED (Y,Gd)₃(Al,Ga)₅O₁₂:Ce Orange to red(Tb,Gd)₃(Al,Ga)₅O₁₂:Ce phosphor of the (Sr,Ba,Ca,Mg,Eu)₂SiO₄ inventionEu-activated α-SiAlON (Ca,Sr,Ba)Si₂N₂O₂:Eu Ca₂BO₃Cl:Eu c)White-light-emitting device including combination of blue LED, one ortwo or more phosphors selected from green phosphors shown in Table, andorange to red phosphor of the invention Semiconductor light- Orange tored emitting element Green phosphor phosphor Blue LEDCa₃(Se,Mg)₂Si₃O₁₂:Ce Orange to red (Ba,Sr)₂SiO₄:Eu phosphor of the(Ca,Sr)Sc₂O₄:Ce invention (Ca,Sr,Ba)Si₂N₂O₂:Eu (Ba,Sr)₃Si₆O₁₂N₂:Eu(Ba,Sr)₃Si₆O₉N₄:Eu (Sr,Ba,Ca)Ga₂S₄:Eu Eu-activated β-SiAlON d)White-light-emitting device including combination of blue LED, one ortwo or more phosphors selected from green phosphors shown in Table,orange to red phosphor of the invention, and dark-red phosphor shown inTable Semiconductor light- Orange to red Dark-red emitting element Greenphosphor phosphor phosphor Blue LED Ca₃(Sc,Mg)₂Si₃O₁₂:Ce Orange to red(Ca,Sr)AlSiNi₃:Eu (Ba,Sr)₂SiO₄:Eu phosphor of the (Ca,Mg)AlSiNi₃:Eu(Ca,Sr)Sc₂O₄:Ce invention (Ca,Sr,Ba)Si₂N₂O₂:Eu (Ba,Sr)₃Si₆O₁₂N₂:Eu(Ba,Sr)₃Si₆O₉N₄:Eu (Sr,Ba,Ca)Ga₂S₄:Eu Eu-activated β-SiAlON

TABLE 3 e) Orange to red light-emitting device including combination ofnear-ultraviolet LED and orange to red phosphor of the inventionSemiconductor light- emitting element Orange to red phosphorNear-ultraviolet LED Orange to red phosphor of the invention f)White-light-emitting device including combination of near-ultravioletLED, one or two or more phosphors selected from blue-green phosphorsshown in Table, and orange to red phosphor of the inventionSemiconductor light- emitting element Blue-green phosphor Orange to redphosphor Near-ultraviolet LED 2SrO•0.84P₂O₅•0.16B₂O₃:Eu Orange to redphosphor Sr₂Si₃O₈•2SrCl₂:Eu of the invention g) White-light-emittingdevice including combination of near-ultraviolet LED, one or two or morephosphors selected from blue phosphors shown in Table, one or two ormore phosphors selected from green phosphors shown in Table, and orangeto red phosphor of the invention Orange Semiconductor light- to redemitting element Blue phosphor Green phosphor phosphor Near-ultravioletLED BaMgAl₁₀O₁₇:Eu Ca₃(Sc,Mg)₂Si₃O₁₂:Ce Orange Ba₃MgSi₂O₈:Eu(Ba,Sr)₂SiO₄:Eu to red (Sr,Ca.Ba,Mg)₅(PO₄)₃Cl:Eu (Ca,Sr)Sc₂O₄:Cephosphor Ce-activated α-SiAlON (Ca,Sr,Ba)Si₂N₂O₂:Eu of the2SrO•0.84P₂O₆•0.16B₂O₃:Eu (Ba,Sr)₃Si 

 O₁₂N₂:Eu invention Sr₂Si₃O₈•2SrCl₂:Eu (Ba,Sr)₂Si 

 O 

 N₄:Eu La_(1−x−y)Ce_(x)Ca_(y)Al(Si_(6−z)Al_(z))(N_(10−z)O_(z))(Sr,Ba,Ca)Ga₂S₄:Eu wherein 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, Eu-activated β-SiAlON 0≦ z ≦ 6 BaMgAl₁₀O₁₇:Eu,Mn SrSi₉Al₁₉ON₃₁:Eu (Sr,Ca,Ba)Al₂O₄:EuEuSi₉Al₁₉ON₃₁ (Sr,Ca,Ba)₄Al₁₄O₂₅:Eu ZnS:Cu,Al ZnS:Au,Cu,Al2SrO•0.84P₂O₅•0.16B₂O₃:Eu Sr₂Si₃O₈•2SrCl₂:Eu

indicates data missing or illegible when filed

TABLE 4 h) White-light-emitting device including combination ofnear-ultraviolet LED, one or two or more phosphors selected from bluephosphors shown in Table, one or two or more phosphors selected fromgreen phosphors shown in Table, orange to red phosphor of the invention,and one or two or more phosphors selected from dark-red phosphors shownin Table Semiconductor light- Orange to red Dark-red emitting elementBlue phosphor Green phosphor phosphor phosphor Near-ultraviolet LEDBaMgAl₁₀O₁₇:Eu Ca₃(Sc,Mg)₂Si₃O₁₂:Ce Orange to red 3.5MgO•0.5MgF₂•GeO₂:MnBa₃MgSi₂O₈:Eu (Ba,Sr)₂SiO₄:Eu phosphor of La₂O₂S:Eu(Sr,Ca,Ba,Mg)₅(PO₄)₃Cl:Eu (Ca,Sr)Sc₂O₄:Ce the invention(Ca,Sr)AlSiNi₃:Eu 2SrO•0.84P₂O₅•0.16B₂O₃:Eu (Ca,Sr,Ba)Si₂N₂O₂:EuSr₂Si₃O 

 •2SrCl₂:Eu (Ba,Sr)₃Si 

 O₁₂N₂:Eu Ce-activated α-SiAlON (Ba,Sr)₃Si 

 O 

 N₄:Eu LaAl(Si_(6−z)Al_(z))N_(10−z)O_(z):Ce (Sr,Ba,Ca)Ga₂S₄:EuLa_(1−x−y)Ce_(x)Ca_(y)Al(Si_(6−z)Al_(z))(N_(10−z)O_(z)) Eu-activatedβ-SiAlON wherein 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, BaMgAl₁₀O₁₇:Eu,Mn 0 ≦ z ≦ 6(Sr,Ca,Ba)Al₂O₄:Eu SrSi₉Al₁₉ON₃₁:Eu (Sr,Ca,Ba)₄Al₁₄O₂₅:Eu EuSi₉Al₁₉ON₃₁ZnS:Cu,Al ZnS:Au,Cu,Al 2SrO•0.84P₂O₅•0.16B₂O₃:Eu Sr₂Si₃O₈•2SrCl₂:Eu

indicates data missing or illegible when filed

Among these combinations, particularly preferably, the light-emittingdevices include combinations of semiconductor light-emitting elementsand phosphors described in Tables 1) to 7).

TABLE 5 1) Semiconductor light- emitting element Orange phosphor BlueLED Orange phosphor of the invention 2) Semiconductor light- emittingelement Red phosphor Blue LED Red phosphor of the invention 3)Semiconductor light- emitting element Yellow phosphor Orange to redphosphor Blue LED (Y,Gd)₃(Al,Ga)₅O₁₂:Ce Orange to red phosphor of theinvention Blue LED (Tb,Gd)₃(Al,Ga)₅O₁₂:Ce Orange to red phosphor of theinvention Blue LED (Sr,Ba,Ca,Mg,Eu)₂SiO₄ Orange to red phosphor of theinvention Blue LED (Ca,Sr,Ba)Si₂N₂O₂:Eu Orange to red phosphor of theinvention 4) Semiconductor light- emitting element Green phosphor Orangeto red phosphor Blue LED Ca₃(Sc,Mg)₂Si₃O₁₂:Ce Orange to red phosphor ofthe invention Blue LED (Ba,Sr)₂SiO₄:Eu Orange to red phosphor of theinvention Blue LED (Ca,Sr)Sc₂O₄:Ce Orange to red phosphor of theinvention Blue LED (Ca,Sr,Ba)Si₂N₂O₂:Eu Orange to red phosphor of theinvention Blue LED (Sr,Ba,Ca)Ga₂S₄:Eu Orange to red phosphor of theinvention Blue LED (Ba,Sr)₃Si₆O₁₂N₂:Eu Orange to red phosphor of theinvention 5) Semiconductor light- Dark-red emitting element Bluephosphor Orange to red phosphor phosphor Blue LED Ca₃(Sc,Mg)₂Si₃O₁₂:CeOrange to red phosphor of (Ca,Sr)AlSiNi₃:Eu the invention Blue LED(Ba,Sr)₂SiO₄:Eu Orange to red phosphor of (Ca,Sr)AlSiNi₃:Eu theinvention Blue LED (Ca,Sr)Sc₂O₄:Ce Orange to red phosphor of(Ca,Sr)AlSiNi₃:Eu the invention Blue LED (Ca,Sr,Ba)Si₂N₂O₂:Eu Orange tored phosphor of (Ca,Sr)AlSiNi₃:Eu the invention Blue LED(Sr,Ba,Ca)Ga₂S₄:Eu Orange to red phosphor of (Ca,Sr)AlSiNi₃:Eu theinvention Blue LED (Ba,Sr)₃Si₆O₁₂N₂:Eu Orange to red phosphor of(Ca,Sr)AlSiNi₃:Eu the invention

TABLE 6 6) Semiconductor light- emitting element Blue phosphor Greenphosphor Orange to red phosphor Near-ultraviolet LED BaMgAl₁₀O₁₇:EuCa₃(Sc,Mg)₂Si₃O₁₂:Ce Orange to red phosphor of the inventionNear-ultraviolet LED BaMgAl₁₀O₁₇:Eu (Ca,Sr)Sc₂O₄:Ce Orange to redphosphor of the invention Near-ultraviolet LED BaMgAl₁₀O₁₇:Eu(Ba,Sr)₂SiO₄:Eu Orange to red phosphor of the invention Near-ultravioletLED BaMgAl₁₀O₁₇:Eu (Ca,Sr,Ba)Si₂N₂O₂:Eu Orange to red phosphor of theinvention Near-ultraviolet LED BaMgAl₁₀O₁₇:Eu 2SrO•0.84P₂O₅•0.16B₂O₃:EuOrange to red phosphor of the invention Near-ultraviolet LEDBaMgAl₁₀O₁₇:Eu Sr₂Si₃O₈•2SrCl₂:Eu Orange to red phosphor of theinvention Near-ultraviolet LED (Sr,Ca,Ba,Mg)₅(PO₄)₃Cl:Eu (Ba,Sr)₂SiO₄:EuOrange to red phosphor of the invention Near-ultraviolet LEDBaMgAl₁₀O₁₇:Eu (Ba,Sr)₃Si 

 O₁₂N₂:Eu Orange to red phosphor of the invention Near-ultraviolet LED(Sr,Ca,Ba,Mg)₅(PO₄)₃Cl:Eu (Ba,Sr)₃Si 

 O₁₂N₂:Eu Orange to red phosphor of the invention 7) Semiconductorlight- Dark-red emitting element Blue phosphor Green phosphor Orange tored phosphor phosphor Near-ultraviolet LED BaMgAl₁₀O₁₇:EuCa₃(Sc,Mg)₂Si₃O₁₂:Ce Orange to red phosphor 3.5MgO•0.5MgF₂•GeO₂:Mn ofthe invention Near-ultraviolet LED BaMgAl₁₀O₁₇:Eu (Ba,Sr)₂SiO₄:Eu Orangeto red phosphor 3.5MgO•0.5MgF₂•GeO₂:Mn of the invention Near-ultravioletLED BaMgAl₁₀O₁₇:Eu (Ca,Sr,Ba)Si₂N₂O₂:Eu Orange to red phosphor3.5MgO•0.5MgF₂•GeO₂:Mn of the invention Near-ultraviolet LEDBaMgAl₁₀O₁₇:Eu 2SrO•0.84P₂O₅•0.16B₂O₃:Eu Orange to red phosphor3.5MgO•0.5MgF₂•GeO₂:Mn of the invention Near-ultraviolet LEDBaMgAl₁₀O₁₇:Eu Sr₂Si₃O₈•2SrCl₂:Eu Orange to red phosphor3.5MgO•0.5MgF₂•GeO₂:Mn of the invention Near-ultraviolet LED(Sr,Ca,Ba,Mg)₅(PO₄)₃Cl:Eu (Ba,Sr)₂SiO₄:Eu Orange to red phosphor3.5MgO•0.5MgF₂•GeO₂:Mn of the invention Near-ultraviolet LEDBaMgAl₁₀O₁₇:Eu (Ba,Sr)₃Si 

 O₁₂N₂:Eu Orange to red phosphor 3.5MgO•0.5MgF₂•GeO₂:Mn of the inventionNear-ultraviolet LED (Sr,Ca,Ba,Mg)₅(PO₄)₃Cl:Eu (Ba,Sr)₃Si 

 O₁₂N₂:Eu Orange to red phosphor 3.5MgO•0.5MgF₂•GeO₂:Mn of the invention

indicates data missing or illegible when filed

The phosphor of the present invention may be used as a mixture of thephosphor of the present invention and another phosphor (wherein the term“mixture” indicates that the phosphors need not necessarily be mixedwith each other but different phosphors are combined). In particular,the phosphors are mixed in the combinations described above to obtainpreferred phosphor mixtures. The types and proportions of the phosphorsmixed are not particularly limited.

<Sealing Material>

The light-emitting device of the present invention usually includes thefirst and/or second phosphor dispersed in a liquid medium serving as asealing material. The same liquid media described in“{Phosphor-Containing Composition}” may be used.

To adjust the refractive index of a sealing member, the liquid mediummay contain a metal element which can form a metal oxide with a highrefractive index. Examples of the metal element which can form a metaloxide with a high refractive index include Si, Al, Zr, Ti, Y, Nb, and B.These metal elements may be used alone or in combination of two or morein any proportion.

The existence form of such a metal element is not particularly limitedunless the transparency of the sealing member is reduced. For example,the metal element may form metalloxane bonds to form a uniform glasslayer. Alternatively, the metal element in the form of particles may bepresent in the sealing member. In the case where the metal element ispresent in the form of particles, the internal structure of eachparticle may be amorphous or crystalline. To obtain a high refractiveindex, a crystal structure is preferred. The particle size is usuallyequal to or lower than the emission wavelength of a semiconductorlight-emitting element, preferably 100 nm or less, more preferably 50 nmor less, and particularly preferably 30 nm or less, in order not toreduce the transparency of the sealing member. For example, theincorporation of particles of, for example, silicon oxide, aluminumoxide, zirconium oxide, titanium oxide, yttrium oxide, or niobium oxideinto a silicone material allows the sealing member to contain the metalelement being in the form of particles.

The liquid medium may further contain known additives such as adiffusing agent, a filler, a viscosity-adjusting agent, and anultraviolet-ray absorber.

<Structure of Light-Emitting Device (Other)>

The structure of the light-emitting device of the present invention isnot particularly limited as long as it includes the first illuminant andthe second illuminant. Usually, the first illuminant and the secondilluminant are arranged on an appropriate frame. In this case, the firstilluminant and the second illuminant are arranged in such a manner thatthe second illuminant is excited by the emission of the first illuminant(i.e., the first and the second phosphors are excited) to emit light andthat light emitted from the first illuminant and/or light emitted fromthe second illuminant is guided to the outside. In this case, the firstphosphor and the second phosphor need not necessarily be incorporated inthe same layer. Phosphors that emit light of different colors may beincorporated into different layers. For example, a layer containing thesecond phosphor may be stacked on a layer containing the first phosphor.

The light-emitting device of the present invention may further include amember other than the excitation light source (first illuminant), thephosphor (second illuminant), and the frame. An example thereof is thesealing material described above. The sealing material can be used todisperse the phosphor (second illuminant) in the light-emitting device.Furthermore, the sealing material can be used to bond the excitationlight source (first illuminant), the phosphor (second illuminant), andthe frame.

<Embodiment of Light-Emitting Device>

While the light-emitting device of the present invention will bedescribed in further detail below by embodiments, the present inventionis not limited to the embodiments described below. Various changes maybe made without departing from the scope of the invention.

FIG. 1 is a schematic perspective view illustrating the positionalrelationship between a first illuminant serving as an excitation lightsource and a second illuminant being formed as a phosphor-containingportion containing the phosphor according to an embodiment of alight-emitting device of the present invention. In FIG. 1, referencenumeral 1 denotes the phosphor-containing portion (second illuminant),reference numeral 2 denotes a surface-emitting GaN-based LD serving asthe excitation light source (first illuminant), and reference numeral 3denotes a substrate. To bring the components into contact with eachother, the LD (2) and the phosphor-containing portion (secondilluminant) (1) may be separately formed, and then their surfaces may bebrought into contact with each other using an adhesive or another means.Alternatively, the phosphor-containing portion (second illuminant) maybe deposited (formed) on the light-emitting face of the LD (2). Thereby,the contact between the LD (2) and the phosphor-containing portion(second illuminant) (1) can be established.

In the case of such a device structure, a light quantity loss in whichlight from the excitation light source (first illuminant) is reflectedfrom the film surface of the phosphor-containing portion (secondilluminant) to emerge to the outside can be inhibited, therebyincreasing luminous efficiency of the entire device.

FIG. 2( a) illustrates a typical shell-shaped light-emitting device andis a schematic cross-sectional view of the light-emitting deviceincluding an excitation light source (first illuminant) and aphosphor-containing portion (second illuminant) according to anembodiment. In the light-emitting device (4), reference numeral 5denotes a mount lead, reference numeral 6 denotes an inner lead,reference numeral 7 denotes an excitation light source (firstilluminant), reference numeral 8 denotes a phosphor-containing resinportion, reference numeral 9 denotes a conductive wire, and referencenumeral 10 denotes a mold member.

FIG. 2( b) illustrates a typical surface-mount light-emitting device andis a schematic cross-sectional view of the light-emitting deviceincluding an excitation light source (first illuminant) and aphosphor-containing portion (second illuminant) according to anembodiment. In the figure, reference numeral 22 denotes an excitationlight source (first illuminant), reference numeral 23 denotes aphosphor-containing resin portion serving as a phosphor-containingportion (second illuminant), reference numeral 24 denotes a frame,reference numeral 25 denotes a conductive wire, reference numerals 26and 27 denote electrodes.

<Application of Light-Emitting Device>

Applications of the light-emitting device of the present invention arenot particularly limited. The light-emitting device can be used invarious fields in which common light-emitting devices are used. Inparticular, the light-emitting device of the present invention issuitably used as a light source of a lighting system and an imagedisplay because of its wide color reproduction range and its high colorrendering properties.

{Lighting System}

In the case where a light-emitting device of the present invention isapplied to a lighting system, the light-emitting device as describedabove may be appropriately incorporated into the known lighting system.An example thereof is a surface-emitting lighting system (11) includingthe light-emitting device (4) shown in FIG. 3.

FIG. 3 is a schematic cross-sectional view of a lighting systemaccording to an embodiment of the present invention. As shown in FIG. 3,in the surface-emitting lighting system, many light-emitting devices(13) (corresponding to the light-emitting device (4) described above)are arranged on the bottom of an opaque square case (12) having a smoothwhite inner surface or the like, and a power supply, a circuit, and thelike (not shown) for driving the light-emitting devices (13) arearranged outside the case. To uniformize emission, a diffuser (14)formed of, for example, a milky white acrylic board is fixed to aportion corresponding to a lid of the case (12).

In the case where the surface-emitting lighting system (11) is driven, avoltage is applied to the excitation light sources (first illuminants)of the light-emitting devices (13) to emit light. The phosphor in thephosphor-containing resin portions serving as the phosphor-containingportions (second illuminants) partially absorb the light and then emitvisible light. The color mixture of the visible light and blue light notabsorbed by the phosphor results in light with high color renderingproperties. The light travels upward in the figure through the diffuser(14). Thereby, illuminating light having uniform brightness is obtainedin the plane of the diffuser (14) of the case (12).

{Image Display}

In the case where a light-emitting device of the present invention isused as a light source of an image display, a specific structure of theimage display is not limited. The light-emitting device is preferablyused together with a color filter. For example, in the case where acolor image display including a color liquid crystal display element isproduced as the image display, a combination of the light-emittingdevice as a backlight, a liquid crystal light valve, and a color filterincluding red, green, and blue pixels produces an image display.

EXAMPLES

While the present invention will be described in further detail below byexamples, the present invention is not limited to examples describedbelow within a range in which the scope of the invention is notimpaired.

In each of examples and comparative examples, various evaluations weremade by the following methods.

Measurement of Change in Weight and Melting Point

A change in weight was measured by heating 10 mg of an alloy powder or anitrogen-containing alloy in each of the examples and comparativeexamples from room temperature to 1,500° C. at a heating rate of 10°C./min under a stream of an atmospheric gas (nitrogen, argon, or a mixedgas of nitrogen and argon) at a flow rate of 100 mL/min with athermogravimetry-differential thermal analyzer (TG-DTA) (TG-DTA2000,manufactured by Bruker AXS K.K.).

In graphs showing the measurement results (FIGS. 5 and 10), the leftvertical axis indicates the sample temperature (° C.), and the rightvertical axis indicates the rate of weight change (%/hr).

Furthermore, in the TG-DTA measurement in an argon flow, an endothermdue to melting was detected, the temperature at which an endothermicpeak appeared was defined as the melting point. In the melting pointmeasurement, temperature calibration was performed with Au (m.p. 1,063°C.) and Si (m.p. 1,410° C.)

Measurement of Rate of Weight Increase

The rate of weight increase was determined by measuring the weight of analloy powder before the primary nitridation step and the weight of anitrogen-containing alloy after the primary nitridation step andcalculating the rate from the formula [4]:

(Weight of nitrogen-containing alloy after primary nitridationstep−weight of alloy powder before primary nitridation step)/weight ofalloy powder before primary nitridation step×100  [4].

Measurement of Total Content of Metal Elements

The total content of metal elements was determined by measuring theweight of an alloy powder before the primary nitridation step and theweight of a nitrogen-containing alloy after the primary nitridation stepand calculating the total content from the formula [5]:

The total content of metal elements (wt %)=100−{(weight ofnitrogen-containing alloy after primary nitridation step−weight of alloybefore primary nitridation step)/weight of nitrogen-containing alloyafter primary nitridation step}×100  [5].

Measurement of Nitrogen Content

The nitrogen content can be determined by measuring the nitrogen contentof a nitrogen-containing alloy or a phosphor with an oxygen-nitrogenanalyzer (manufactured by Leco Corporation) and calculating the nitrogencontent of the nitrogen-containing alloy from the formula [6] orcalculating the nitrogen content of the phosphor from the formula [6A]:

Nitrogen content of nitrogen-containing alloy (wt %)=(amount ofnitrogen/weight of nitrogen-containing alloy)×100  [6]

Nitrogen content of phosphor (wt %)=(amount of nitrogen/weight ofphosphor)×100  [6A]

Measurement of Oxygen Content

The oxygen content can be determined by measuring the oxygen content ofa nitrogen-containing alloy or a phosphor with an oxygen-nitrogenanalyzer (manufactured by Leco Corporation) and calculating the oxygencontent of the nitrogen-containing alloy from the formula [8] orcalculating the oxygen content of the phosphor from the formula [8A]:

Oxygen content of nitrogen-containing alloy (wt %)=(amount ofoxygen/weight of nitrogen-containing alloy)×100  [8]

Oxygen content of phosphor (wt %)=(amount of oxygen/weight ofphosphor)×100  [8A]

Calculation Method of NI/NP

NI/NP was determined from the formula [7] using the measurements of thenitrogen content.

0.03≦NI/NP≦0.9  [7]

wherein in the formula [7],

NI represents the nitrogen content (% by weight) of anitrogen-containing alloy; and

NP represents the nitrogen content (% by weight) of a phosphor produced.

Measurement of Weight-Average Median Diameter D₅₀ of Alloy Powder

An alloy powder sample was dispersed in ethylene glycol. The weightparticle-size distribution curve of the sample was determined with alaser scattering particle size distribution analyzer (LA-300,manufactured by HORIBA, Ltd.) in the particle size range of 0.1 μm to600 μm at an ambient temperature of 25° C. and a humidity of 70%. Aparticle size corresponding to an integrated value of 50% was defined asthe weight-average median diameter D₅₀. Furthermore, QD was calculatedfrom the expression: QD=(D₇₅−D₂₅)/(D₇₅+D₂₅) where D₂₅ represents aparticle size corresponding to an integrated value of 25%, and D₇₅represents a particle size corresponding to an integrated value of 75%.

Measurement of Weight-Average Median Diameter D₅₀ of Phosphor

Prior to measurement, a sample was dispersed by ultrasound with anultrasonic dispersion system (manufactured by Kaijo Corporation) at afrequency of 19 KHz and an ultrasound intensity of 5 W for 25 seconds.Water containing a minute amount of a surfactant to preventreaggregation was used as a dispersing liquid.

The weight-average median diameter was measured with a laserdiffraction/scattering particle size distribution analyzer (manufacturedby HORIBA, Ltd).

[X-Ray Powder Diffraction Measurement]

X-ray powder diffraction was performed with a powder X-raydiffractometer XPert MPD (manufactured by Philips) in air. Measurementconditions are described below.

Scan step [° 2θ]: 0.0500

Start position [° 2θ]: 10.0350

Finish position [° 2θ]: 89.9350

Predetermined X-ray output: 45 kV, 40 mA

Divergence slit (DS) size [°]: 1.0000

Receiving slit (RS) size [mm]: 1.0000

Type of scanning: Continuous

Scan step time [s]: 33.0000

Temperature during measurement [° C.]: 0.00

Diameter of goniometer [mm]: 200.00

Focus-DS distance [mm]: 91.00

Irradiation width [mm]: 10.00

Sample width [mm]: 10.00

Scan axis: goniometer

Incident side monochromater: None

Target: Cu

CuKα (1.541 Å)

Analysis of Chemical Composition

The chemical composition was analyzed by inductively coupledplasma-atomic emission spectrometry (hereinafter, also referred to as an“ICP technique”) with an ICP chemical analyzer “JY 38S” (manufactured byJobin-Yvon).

Measurement of Electric Conductivity of Supernatant Liquid inWater-Dispersing Test

Phosphor particles were classified by sieving so as to have aweight-average median diameter D₅₀ of 9 μm (however, if washed phosphorparticles had a weight-average median diameter D₅₀ of 9 μm, thisoperation was not performed). The phosphor particles were placed inwater weighing ten times as much as the phosphor and stirred with astirrer for 10 minutes so as to be dispersed. The dispersion was allowedto stand for 1 hour, leading to spontaneous sedimentation of thephosphor. The electric conductivity of the supernatant liquid wasmeasured.

The electric conductivity was measured with a conductivity meter “ECMETER CM-30G”, manufactured by DKK-TOA Corporation. Washing andmeasurement were performed at room temperature.

The water used in the water-dispersing test for phosphors or used towash the phosphors in examples and comparative examples had an electricconductivity of 0.03 mS/m.

Emission Spectrum

The emission spectrum of a phosphor was measured with a fluorescencespectrometer (manufactured by JASCO Corporation) including a 150-W xenonlamp as an excitation light source and a CCD multichannel detector C7041(manufactured by Hamamatsu Photonics K.K.) as a spectrometer. Light froman excitation light source was passed through a grating spectrometerwith a focal length of 10 cm. The phosphor was irradiated with onlyexcitation light having a wavelength of 465 nm through an optical fiber.Light emitted from the phosphor by irradiation with the excitation lightwas dispersed into a spectrum with a grating spectrometer having a focallength of 25 cm. Light emission intensities at wavelengths in the rangeof 300 nm to 800 nm were measured with a spectrometer. Signal processingsuch as sensitivity correction with a personal computer was performed toobtain an emission spectrum.

Measurement of Peak Emission Wavelength, Relative Peak EmissionIntensity, and Relative Brightness

The peak emission wavelength was read from the resulting emissionspectrum.

The relative peak emission intensity (hereinafter, also referred to as“peak emission intensity”) was expressed as a relative value withreference to the peak intensity of a phosphor in Reference Example 1.

The relative brightness with respect to 100% of the stimulus value Y ofthe phosphor in Reference Example 1 (hereinafter, also referred tosimply as “brightness”) was calculated from a stimulus value Y in theXYZ colorimetric system calculated in accordance with JIS Z8724. Thebrightness was measured while excitation blue light was being blocked.

Reference Example 1

Ca₃N₂ (manufactured by CERAC Inc., 200-mesh passed), AlN (F grade,manufactured by Tokuyama Corp.), Si₃N₄ (SN-E10, manufactured by UbeIndustries, Ltd.), and Eu₂O₃ (manufactured by Shin-Etsu Chemical Co.Ltd.) were weighed in an argon atmosphere in such a manner that theratio of Eu to Ca to Al to Si=0.008:0.992:1:1 (molar ratio). Thesematerials were mixed using an alumina mortar. The resulting raw materialmixture was placed in a boron nitride crucible. The Crucible was placedin an atmosphere furnace. After the furnace was evacuated to 1×10⁻² Pa,the evacuation was stopped. Nitrogen was charged into the furnace insuch a manner that the pressure in the furnace was increased to 0.1 MPa.The mixture was heated to 1,600° C. and maintained at 1,600° C. for 5hours. The resulting fired product was milled with an alumina mortar.The resulting particles each having a size of 100 μm or less werecollected to prepare a phosphor. The phosphor had a peak emissionwavelength of 648 nm at an excitation wavelength of 465 nm.

Measurement of Chromaticity Coordinates

Chromaticity coordinates x and y in the XYZ colorimetric system definedby JIS Z8701 were calculated from the data in the wavelength range of480 nm to 800 nm of an emission spectrum.

Calculation of Value of Formula [A]

The mass (g) of a firing vessel and the mass (g) of a raw material for aphosphor were measured. The resulting measurements were substituted forthe formula [A] to yield the value of the formula [A]:

(Mass of raw material for phosphor)/{(mass of firing vessel)+(mass ofraw material for phosphor)}  [A].

Measurement of Temperature Change Per Minute in Heating Step

The temperature of the external wall of a firing vessel was measured atintervals of 10 seconds with a tungsten-rhenium alloy thermocouple. Athermometer was arranged on the external wall of the firing vessel at aheight position approximately equal to half the height of a raw materialfor a phosphor placed therein. The temperature change per minute wasdetermined from the formula [B] using the measurements:

Temperature change (° C./min)=temperature at time T min−temperature attime (T−1) min  [B].

Example 1 Production of Alloy

Raw material metals were weighed in such a manner that the compositionratio of metal elements, i.e., the ratio (molar ratio) of Al to Si, was1:1. The raw material metals were charged into a graphite crucible andmelted in an argon atmosphere with a high-frequency induction meltingfurnace. The molten metal mixture was poured from the crucible into amold and then solidified, whereby an alloy (a mother alloy) in which thecomposition ratio of the metal elements, i.e., the ratio of Al to Si,was 1:1, was obtained.

The mother alloy and other raw material metals were weighed in such amanner that the ratio of Eu to Sr to Ca to Al to Si was0.008:0.792:0.2:1:1 (molar ratio). After the furnace was evacuated, theevacuation of the furnace was stopped and argon was then introduced intothe furnace until the pressure in the furnace reached a predeterminedvalue. The mother alloy was melted in a calcia crucible. Sr, Eu, and Ca,which are the raw material metals, were added thereto. After all thesecomponents were melted into a mixture and the molten mixture wasobserved to have been agitated by an induction current, the moltenmixture was poured from the crucible into a water-cooled copper mold(having a plate shape with a thickness of 40 mm) and then solidified.

A 40-mm-thick plate of the resulting alloy was analyzed with regard toits composition by an ICP technique. About 10 g of a sample was takenfrom a portion close to the center of gravity of the plate and a 10 g ofa sample was taken from an end portion of the plate. The elementalanalysis of the samples using the ICP technique determined that

the ratio of Eu to Sr to Ca to Al to Si in the sample taken from theplate center portion was 0.009:0.782:0.212:1:0.986; and

the ratio of Eu to Sr to Ca to Al to Si in the sample taken from theplate end portion was 0.009:0.756:0.210:1:0.962.

The samples had substantially the same composition within the scope ofanalytical precision. Therefore, Eu and the other elements seemed to beuniformly distributed.

The resulting alloy had an X-ray powder diffraction pattern similar tothat of Sr(Si_(0.5)Al_(0.5))₂ and therefore was determined to be anAlB₂-type intermetallic compound referred to as an alkaline-earthsilicide.

Milling Step

The resulting alloy was milled with an alumina mortar in a nitrogenatmosphere in such a manner that the formed particles had a diameter ofabout 1 mm or less. The resulting alloy powder was milled in a nitrogenatmosphere (having an oxygen content of 2% by volume) with a supersonicjet mill (PJM-80SP, manufactured by Nippon Pneumatic manufacturing Co.,Ltd.) under the following conditions: a milling pressure of 0.15 MPa anda feed rate of 0.8 kg/hr.

The weight-average median diameter D₅₀, QD, and the particle sizedistribution of the resulting alloy powder were measured. Theweight-average median diameter D₅₀ was 14.2 μm. The QD was 0.38. Thepercentage of alloy particles having a size of 10 μm or less in thealloy powder was 28.6% of the total. The percentage of alloy particleshaving a size of 45 μm or more was 2.90. The alloy powder had an oxygencontent of 0.3% by weight and a nitrogen content of 0.3% by weight orless (limit of detection).

The melting point of the resulting alloy powder was measured under argonflow. The melting initiation temperature was about 1,078° C., and themelting point was 1,121° C.

Primary Nitridation Step

Into a boron nitride crucible with an inner diameter of 54 mm, 40 g ofthe resulting alloy powder was placed. The alloy powder was heated fromroom temperature to 950° C. at a heating rate of 4° C./min, heated from950° C. to 1,100° C. at a heating rate of 2° C./min, and maintained atthe maximum temperature (1,100° C.) for 5 hours in a tubular electricfurnace under a stream of a nitrogen-containing argon gas(nitrogen:argon=2:98 (volume ratio)) at a flow rate of 2 L/min underambient pressure. Then the alloy powder was cooled to 950° C. at acooling rate of 5° C./min and left to cool to room temperature at acooling rate of about 10° C./min under a stream of a nitrogen-containingargon gas (nitrogen:argon=2:98 (volume ratio)) at a flow rate of 2L/min, thereby producing a nitrogen-containing alloy.

The resulting nitrogen-containing alloy was taken out and weighed. Therate of weight increase was 4.5% by weight. The total metal elementcontent was 95.7% by weight. Furthermore, the nitrogen content and theoxygen content of the resulting nitrogen-containing alloy weredetermined by the foregoing method. Table 7 shows the results.

The temperature in the primary nitridation step of the present inventionindicates the temperature in the furnace, i.e., a preset temperature ofa firing apparatus. The same is true in examples and comparativeexamples described below.

Secondary Nitridation Step

The nitrogen-containing alloy prepared in the primary nitridation stepwas milled with an alumina mortar under a stream of nitrogen so as to begiven a particle size of 53 μm or less. Undersize particles of the alloythat passed through a sieve with 53-μm openings were collected. Thealloy powder was placed into a boron nitride crucible with an innerdiameter of 54 mm. The boron nitride crucible was set in a hot isostaticpress (HIP). The press was evacuated to 5×10⁻¹ Pa. The alloy powder washeated to 300° C. The evacuation was continued for one hour at 300° C.Nitrogen was charged into the press in such a manner that the pressurein the press was increased to 1 MPa. The alloy powder was cooled toabout room temperature. The pressure in the press was reduced to 0.1MPa. Nitrogen was introduced into the press again in such a manner thatthe pressure in the press was increased to 1 MPa. This procedure wasrepeated twice. The pressure in the press was adjusted to about 0.1 MPabefore initiation of heating. The alloy powder was heated until thetemperature in the furnace reached 950° C. at a heating rate of 600°C./hr. At this point, the internal pressure was increased to about 0.5MPa. The temperature in the furnace was increased from 950° C. to 1,100°C. at a heating rate of 66.7° C./hr. Then the temperature was maintainedat 1,100° C. for 30 minutes. The nitrogen pressure was increased to 140MPa over a period of about three hours while the temperature wasmaintained at 1,100° C. Heating and pressurization were performed over aperiod of about one hour in such a manner that the temperature in thefurnace was increased to 1,900° C. and the pressure in the furnace wasincreased to 190 MPa. This state was maintained for two hours. The alloypowder was cooled to 400° C. or lower over a period of three hours andthen left to cool. Twelve hours later, a phosphor having a temperatureof about room temperature was obtained. The temperatures described aboveindicate the temperatures in the furnace, in other words, thetemperatures described above indicate preset temperatures of the firingapparatus (HIP in this example) (the same is true in the followingexamples unless otherwise specified).

The resulting phosphor was milled with an alumina mortar. The lightemission properties (peak emission wavelength, relative peak emissionintensity, relative brightness, and chromaticity coordinates) weremeasured. Table 9 shows the results.

In this example, the value of the foregoing formula [A] was 0.50 (vesselmass: 40 g, raw material mass: 40 g), and the temperature change perminute in the heating step was 2° C./min or less.

Example 2 Post-Treatment Step

The phosphor prepared in Example 1 was placed in water weighing tentimes as much as the phosphor at room temperature. The mixture wasstirred for 10 minutes with a stirrer so as to be dispersed. After thedispersion had been allowed to stand for one hour, the precipitation ofthe phosphor was observed. The phosphor was separated by filtration.This procedure was repeated 15 times. The phosphor was dehydrated bysuction filtration. The phosphor was placed in 0.5 N hydrochloric acidweighing ten times as much as the phosphor. The mixture was stirred for10 minutes with the stirrer so as to be dispersed. After the dispersionhad been allowed to stand for one hour, the phosphor was separated byfiltration. The phosphor was dispersed in water weighing ten times asmuch as the phosphor and then filtrated. This procedure was repeatedthree times. The electrical conductivity of a supernatant liquid wasmeasured as described above and determined to be 1.90 mS/m. Afterdehydration, drying was performed at 120° C. for 12 hours to obtain aphosphor.

The weight-average median diameter D₅₀ of the resulting phosphor wasmeasured and determined to be 12.7 μm. The light emission properties ofthe resulting phosphor were measured. Table 9 shows the results. Theresults demonstrate that washing treatment of the phosphor prepared inExample 1 improves the relative emission peak intensity and the relativebrightness. Table 8 shows the value of the formula [A] and thetemperature change per minute in the heating step.

Example 3

The primary nitridation step was performed as in Example 1, except thatthe heating conditions were as follows: the maximum temperature was1,050° C., and the holding time at the maximum temperature was 10 hours.The rate of weight increase and the total metal element content of theresulting nitrogen-containing alloy were calculated. Table 7 shows theresults.

Subsequently, the secondary nitridation step was performed as in Example1 to prepare a phosphor. The light emission properties of the resultingphosphor were measured. Table 9 shows the results. Table 8 shows thevalue of the formula [A] and the temperature change per minute in theheating step.

Example 4

The phosphor prepared in Example 3 was washed with water 15 times andthen with 0.5 N hydrochloric acid once in the same way as in Example 2.Subsequently, the phosphor was washed with water five times in such amanner that the electrical conductivity of a supernatant liquid was 1.52mS/m. The phosphor was subjected to classification to prepare a phosphorhaving a particle diameter in the range of 3 μm to 30 μm.

The weight-average median diameter D₅₀ of the resulting phosphor wasmeasured and determined to be 7.7 μm. The light emission properties ofthe resulting phosphor were measured. Table 9 shows the results. Theresults demonstrate that the resulting phosphor has a relative emissionpeak intensity and a relative brightness higher than those of thephosphor prepared in Example 3. Table 8 shows the value of the formula[A] and the temperature change per minute in the heating step.

Example 5

A nitrogen-containing alloy was prepared as in Example 3, except that inthe primary nitridation step, the heating atmosphere was anitrogen-containing argon gas (nitrogen:argon=7:93 (volume ratio))flowing at a flow rate of 2 L/min. The rate of weight increase and thetotal metal element content of the resulting nitrogen-containing alloywere determined. Table 7 shows the results. The results demonstrate thatin comparison with Example 3, an increase in nitrogen concentration inthe furnace results in an increase in the rate of weight increase and adecrease in the total metal element content.

Subsequently, the secondary nitridation step was performed as in Example1 to prepare a phosphor. The light emission properties of the resultingphosphor were measured. Table 9 shows the results. The resultsdemonstrate that the resulting phosphor has improved light emissionproperties compared with the phosphor prepared in Example 3. Table 8shows the value of the formula [A] and the temperature change per minutein the heating step.

Example 6

A nitrogen-containing alloy was prepared as in Example 3, except that inthe primary nitridation step, the heating atmosphere was anitrogen-containing argon gas (nitrogen:argon=4:96 (volume ratio))flowing at a flow rate of 2 L/min. The rate of weight increase and thetotal metal element content of the resulting nitrogen-containing alloywere determined. Table 7 shows the results.

Subsequently, the secondary nitridation step was performed as in Example1 to prepare a phosphor. The light emission properties of the resultingphosphor were measured. Table 9 shows the results. Table 8 shows thevalue of the formula [A] and the temperature change per minute in theheating step.

Example 7

A nitrogen-containing alloy was prepared as in Example 3, except that inthe primary nitridation step, the heating atmosphere was anitrogen-containing argon gas (nitrogen:argon=5:95 (volume ratio))flowing at a flow rate of 2 L/min, and the holding time at the maximumtemperature (1,050° C.) was five hours. The rate of weight increase andthe total metal element content of the resulting nitrogen-containingalloy were determined. Table 7 shows the results. Subsequently, thesecondary nitridation step was performed as in Example 1 to prepare aphosphor. The light emission properties of the resulting phosphor weremeasured. Table 9 shows the results. Table 8 shows the value of theformula [A] and the temperature change per minute in the heating step.

Example 8

A phosphor was prepared as in Example 3, except that in the primarynitridation step, the heating atmosphere was a nitrogen-containing argongas (nitrogen:argon=5:95 (volume ratio)) flowing at a flow rate of 2L/min. The rate of weight increase and the total metal element contentof the resulting nitrogen-containing alloy were determined. Table 7shows the results.

Subsequently, the secondary nitridation step was performed as in Example1 to prepare a phosphor. The light emission properties of the resultingphosphor were measured. Table 9 shows the results. Table 8 shows thevalue of the formula [A] and the temperature change per minute in theheating step.

Example 9

An alloy powder prepared as in Example 1 was subjected to the primarynitridation step under the following conditions: 40 g of the alloypowder was placed into a boron nitride crucible with an inner diameterof 54 mm and heated in an atmosphere furnace. The alloy powder washeated from room temperature to 900° C. at a heating rate of 20° C./minin vacuum. A nitrogen-containing argon gas (nitrogen:argon=5:95 (volumeratio)) was charged thereinto at 900° C. in such a manner that the gaugepressure of the gas was 0.01 MPa. The alloy powder was heated from 900°C. to 1,050° C. at a heating rate of 2° C./min under a stream of anitrogen-containing argon gas (nitrogen:argon=5:95 (volume ratio)) at aflow rate of 1 L/min while this pressure was maintained. The alloypowder was maintained at the maximum temperature of 1,050° C. for fourhours. Then the alloy powder was cooled to 200° C. or lower over aperiod of about two hours and left to cool to room temperature, therebypreparing a nitrogen-containing alloy. The rate of weight increase andthe total metal element content of the resulting nitrogen-containingalloy were calculated. Table 7 shows the results.

Subsequently, the secondary nitridation step was performed as in Example1 to prepare a phosphor. The light emission properties of the resultingphosphor were measured. Table 9 shows the results. Table 8 shows thevalue of the formula [A] and the temperature change per minute in theheating step.

Example 10

A nitrogen-containing alloy was prepared as in Example 1, except that inthe primary nitridation step, heating was performed in a stream ofnitrogen, the maximum temperature was 1,030° C., and the holding time atthe maximum temperature was eight hours.

Analysis of the resulting nitrogen-containing alloy with regard to itsnitrogen content and its oxygen content demonstrated that the nitrogencontent was 1.10% by weight and the oxygen content was 1.66% by weight.The rate of weight increase was about 3% by weight. The total metalelement content was 97% by weight.

The results of analysis of the nitrogen content and the oxygen contentand analysis by the ICP technique demonstrated that the compositionratio of the elements, i.e., the ratio of Al to Si to Ca to Sr to Eu toN to O, constituting the resulting nitrogen-containing alloy was1:0.922:0.214:0.734:0.008:0.11:0.14.

The resulting nitrogen-containing alloy was subjected to the secondarynitridation step as in Example 1 to prepare a phosphor.

The light emission properties of the resulting phosphor were measured.Table 9 shows the results.

Subsequently, the resulting phosphor was subjected to washing treatmentas in Example 4. The oxygen content, the nitrogen content, and the NI/NPwere determined. Table 9 shows the results. Table 8 shows the value ofthe formula [A] and the temperature change per minute in the heatingstep.

Example 11

A phosphor was prepared as in Example 1, except that the alloy powderprepared in Example 1 was subjected to the primary nitridation stepunder the following conditions and that after the completion of theprimary nitridation step, the milling treatment was not performed.

The atmosphere in a rotary kiln was entirely replaced with argon. Analumina furnace tube having a diameter of 90 mm and a length of 1,500 mmwas set so as to have an angle of inclination of 1.9°. An alloy powderwas continuously fed at a feed rate of 400 g/hr using a screw feederunder a stream of a mixed gas containing nitrogen (0.7 L/min), hydrogen(0.2 L/min), and argon (5 L/min) in the countercurrent direction of thefurnace tube while the furnace tube was rotating at 5 rpm. Thetemperature of a heater was set at 1,100° C. In this case, the residencetime of the alloy powder in a soaking area (here, a middle portion witha length of about 150 mm of the furnace tube) was three minutes. Anitrogen-containing alloy prepared by the primary nitridation step wasejected from the furnace tube, collected in a vessel filled with argon,and rapidly cooled. The resulting nitrogen-containing alloy was in theform of a powder.

Analysis of the resulting nitrogen-containing alloy with regard to itsnitrogen content and its oxygen content demonstrated that the nitrogencontent was 3.7% by weight and the oxygen content was 1.2% by weight.

FIG. 6 shows an X-ray powder diffraction pattern of the resultingnitrogen-containing alloy. The main phase had an X-ray powderdiffraction pattern similar to that of Sr(Si_(0.5)Al_(0.5))₂, which isone of AlB₂-type intermetallic compounds referred to as alkaline-earthsilicides. Other intermetallic compounds such as SrSi (PDF No. 16-0008)and SrSi₂ (PDF No. 19-1285) were also detected.

Subsequently, the resulting nitrogen-containing alloy was subjected tothe secondary nitridation step as in Example 1 to prepare a phosphor.The light emission properties of the resulting phosphor were measured.Table 9 shows the results.

After the resulting phosphor was subjected to washing treatment as inExample 2, the oxygen content and the nitrogen content were determined.Table 9 shows the results. Table 8 shows the value of the formula [A]and the temperature change per minute in the heating step.

Example 12

Into a boron nitride crucible with an inner diameter of 54 mm, 40 g ofthe alloy powder prepared in Example 1. The alloy powder was subjectedto the primary nitridation step in an atmosphere furnace. The alloypowder was heated from room temperature to 900° C. at a heating rate of20° C./min in vacuum. A nitrogen-containing argon gas(nitrogen:argon=5:95 (volume ratio)) was charged thereinto in such amanner that the gauge pressure of the gas was 0.01 MPa. The alloy powderwas heated from 900° C. to 1,050° C. at a heating rate of 2° C./minunder a stream of a nitrogen-containing argon gas (nitrogen:argon=5:95(volume ratio)) at a flow rate of 1 L/min while this pressure wasmaintained. The alloy powder was maintained at the maximum temperatureof 1,050° C. for four hours. After the alloy powder was cooled to 900°C., the atmospheric gas was replaced with nitrogen. The alloy powder washeated from 900° C. to 1,050° C. at a heating rate of 2° C./min and thenmaintained at 1,050° C. for four hours. The sample was cooled to 200° C.over a period of about two hours and left to cool to about roomtemperature.

The oxygen content and the nitrogen content of the resultingnitrogen-containing alloy were calculated. Table 7 shows the results.

FIG. 7 shows an X-ray powder diffraction pattern of the resultingnitrogen-containing alloy. From the X-ray powder diffraction pattern, aphase similar to Sr(Si_(0.5)Al_(0.5))₂ was detected as well asintermetallic compounds such as SrSi (PDF No. 16-0008) and SrSi₂ (No.19-1285).

Subsequently, the resulting nitrogen-containing alloy was subjected tothe secondary nitridation step as in Example 1, except that thenitrogen-containing alloy was heated from room temperature to 1,900° C.at a heating rate of 600° C./hr. Then the resulting phosphor wassubjected to washing treatment and classifying treatment as in Example4. The light emission properties of the resulting phosphor weremeasured. Table 9 shows the results. The oxygen content, the nitrogencontent, and NI/NP were determined. Table 9 also shows the results.Table 8 shows the value of the formula [A] and the temperature changeper minute in the heating step. FIG. 11 shows an X-ray powderdiffraction pattern of the resulting phosphor.

Example 13

Into a boron nitride crucible with an inner diameter of 54 mm, 40 g ofthe alloy powder prepared in Example 1. The alloy powder was subjectedto the primary nitridation step in an atmosphere furnace. The alloypowder was heated from room temperature to 900° C. at a heating rate of20° C./min in vacuum. A nitrogen-containing argon gas(nitrogen:argon=5:95 (volume ratio)) was charged thereinto in such amanner that the gauge pressure of the gas was 0.01 MPa. The alloy powderwas heated from 900° C. to 1,050° C. at a heating rate of 2° C./minunder a stream of a nitrogen-containing argon gas (nitrogen:argon=5:95(volume ratio)) at a flow rate of 1 L/min while this pressure wasmaintained. The alloy powder was maintained at the maximum temperatureof 1,050° C. for three hours. The alloy powder was left to cool to roomtemperature. The alloy powder was heated again from 900° C. to 1,050° C.at a heating rate of 2° C./min under a stream of a nitrogen-containingargon gas (nitrogen:argon=5:95 (volume ratio)) at a flow rate of 1L/min. The alloy powder was maintained at 1,050° C. for three hours. Thealloy powder was cooled to room temperature. The atmosphere was replacedwith nitrogen. The alloy powder was heated again from 900° C. to 1,050°C. at a heating rate of 2° C./min and maintained at 1,050° C. for threehours. The alloy powder was cooled to 200° C. over a period of about twohours and then left to cool to about room temperature.

The oxygen content and the nitrogen content of the resultingnitrogen-containing alloy were calculated. Table 7 shows the results.

FIG. 8 shows an X-ray powder diffraction pattern of the resultingnitrogen-containing alloy. From the X-ray powder diffraction pattern,intermetallic compounds such as SrSi (PDF No. 16-0008) and SrSi₂ (No.19-1285) were detected.

The resulting nitrogen-containing alloy was subjected to the secondarynitridation step as in Example 1, except that 142 g of thenitrogen-containing alloy was placed in a boron nitride crucible with adiameter of 85 mm and heated from room temperature to 1,900° C. at aheating rate of 600° C./hr. Then the resulting phosphor was subjected towashing treatment and classifying treatment as in Example 4. The lightemission properties of the resulting phosphor were measured. Table 9shows the results. The oxygen content, the nitrogen content, and NI/NPwere determined. Table 9 also shows the results. Table 8 shows the valueof the formula [A] and the temperature change per minute in the heatingstep. FIG. 12 shows an X-ray powder diffraction pattern of the resultingphosphor.

Example 14

A phosphor was prepared as in Example 1, except that the alloy powderprepared in Example 1 was subjected to the primary nitridation stepunder the following conditions and that after the completion of theprimary nitridation step, the milling treatment was not performed.

After an atmosphere rotary kiln was entirely evacuated, gas replacementwas performed by introducing a mixed gas of nitrogen (2.5 L/min) andargon (2.5 L/min). An alumina furnace tube having a diameter of 90 mmand a length of 1,500 mm was set so as to have an angle of inclinationof 1.9°. The temperature of a heater was set at 1,100° C. An alloypowder was continuously fed at a feed rate of 220 g/hr using a screwfeeder under a stream of a mixed gas containing nitrogen (0.7 L/min),hydrogen (0.2 L/min), and argon (5 L/min) in the countercurrentdirection of the furnace tube while the furnace tube was rotating at 5rpm. In this case, the residence time of the alloy powder in a soakingarea (time from feed initiation to discharge initiation×soaking arealength/furnace tube length) was about three minutes. Anitrogen-containing alloy prepared by the primary nitridation step wasejected from the furnace tube, collected in a vessel filled with argon,and rapidly cooled.

Analysis of the nitrogen-containing alloy prepared by the primarynitridation step demonstrated that the nitrogen content was 8.9% byweight and the oxygen content was 2.9% by weight.

FIG. 9 shows an X-ray powder diffraction pattern of the resultingnitrogen-containing alloy. FIG. 9 demonstrates that intermetalliccompounds such as SrSi (PDF No. 16-0008) and SrSi₂ (PDF No. 19-1285)were detected.

Subsequently, the resulting nitrogen-containing alloy was subjected tothe secondary nitridation step under the conditions described below. Theabove-described HIP was evacuated to 5×10⁻¹ Pa. The alloy powder washeated to 300° C. Evacuation was continued for one hour at 300° C. Thepressure of the nitrogen atmosphere was increased to about 49 MPa atroom temperature. The nitrogen-containing alloy powder was heated untilthe temperature reached 900° C. at a heating rate of 600° C./hr. Thenitrogen-containing alloy powder was then heated until the temperaturereached 1,100° C. at a heating rate of 66.7° C./hr. At this point, thepressure was about 140 MPa. Heating and pressurization were performedover a period of about 1.5 hours in such a manner that the temperaturein the furnace was increased to 1,900° C. and the internal pressure wasincreased to 190 MPa. This state was maintained for one hour. Thenitrogen-containing alloy powder was left to cool to room temperature,thereby providing a phosphor. The resulting phosphor was disintegratedwith an alumina mortar so as to have a particle diameter of 50 μm orless. The light emission properties were measured. Table 9 shows theresults. Table 8 shows the value of the formula [A] and the temperaturechange per minute in the heating step. After the phosphor was subjectedto washing treatment as in Example 2, analysis of the phosphor withregard to its oxygen content, its nitrogen content, and its NI/NP wasperformed. Table 9 also shows the results.

Example 15

The secondary nitridation step was performed to prepare a phosphor as inExample 14, except that after the primary nitridation step, theresulting nitrogen-containing alloy was milled with an alumina mortar ina nitrogen atmosphere and then screened with a sieve having 53-μmopenings in a nitrogen atmosphere.

The light emission properties of the resulting phosphor were measured asin Example 14. Table 9 shows the results. After the phosphor wassubjected to washing treatment as in Example 2, analysis of the phosphorwith regard to its oxygen content, its nitrogen content, and its NI/NPwas performed. Table 9 also shows the results. Table 8 shows the valueof the formula [A] and the temperature change per minute in the heatingstep.

Example 16

The primary nitridation step was performed as in Example 14, except thatthe feed rate of the alloy powder was set at 71 g/hr, a mixed gascontaining nitrogen (0.25 L/min) and argon (5 L/min) was flowed, and theheat treatment was performed at a heater temperature of 1,080° C. Inthis case, the residence time of the alloy powder in a soaking area(time from feed initiation to discharge initiation×soaking arealength/furnace tube length) was about three minutes. Anitrogen-containing alloy prepared by the primary nitridation step wasejected from the furnace tube, collected in a vessel filled with argon,and rapidly cooled.

Analysis of the nitrogen-containing alloy prepared by the primarynitridation step demonstrated that the nitrogen content was 5.5% byweight and the oxygen content was 2.8% by weight.

The nitrogen-containing alloy was subjected to the secondary nitridationstep as in Example 14 to produce a phosphor. The light emissionproperties of the phosphor were measured as in Example 14. Table 9 showsthe results. After the phosphor was subjected to washing treatment as inExample 2, analysis of the phosphor with regard to its oxygen content,its nitrogen content, and its NI/NP was performed. Table 9 also showsthe results. Table 8 shows the value of the formula [A] and thetemperature change per minute in the heating step.

Example 17

The primary nitridation step was performed as in Example 14, except thata mixed gas of nitrogen (2.5 L/min), argon (2.5 L/min), and hydrogen(0.2 L/min) was fed into the furnace tube from the lower side of theinclined furnace tube while a mixed gas of nitrogen (2.5 L/min) andargon (2.5 L/min) was made to flow in the entire atmosphere rotary kiln,and the feed rate of the alloy powder was set at 0.3 kg/hr.

Analysis of the nitrogen-containing alloy prepared by the primarynitridation step demonstrated that the nitrogen content was 14.4% byweight and the oxygen content was 2.2% by weight.

Subsequently, the resulting nitrogen-containing alloy was milled as inExample 1. The weight-average median diameter D₅₀ of the resulting alloypowder was 11.4 μm. The proportion of alloy particles having a diameterof 45 μm or more was 1% or less. The proportion of alloy particleshaving a diameter of 100 μm or more is less than 0.1%. The proportion ofalloy particles having a diameter of 5 μm or less was 12%. The QD was0.36.

The resulting nitrogen-containing alloy was subjected to nitridationunder the same conditions as described in Example 14. The light emissionproperties were measured as in Example 14. Table 9 shows the results.Table 8 shows the value of the formula [A] and the temperature changeper minute in the heating step.

Example 18

A phosphor was produced under the same conditions as described inExample 17, except that the value of the formula [A] was 0.50 (thefilling rate of the raw material for the phosphor in the firing vesselwas 35% by volume). The light emission properties of the resultingphosphor were measured as in Example 17. Table 9 shows the results.

Example 19

The nitrogen-containing alloy prepared by the primary nitridation stepin Example 17 was disintegrated with an alumina mortar so as to have aparticle diameter of 500 μm or less. The nitrogen-containing alloy wasmilled with a jet mill having a grinding chamber lined with zirconia(Nano Grinding Mill NJ-50, manufactured by Sunrex Kogyo Co., Ltd.) in anitrogen atmosphere (containing 1% by volume or less oxygen) at amilling pressure of 0.3 MPa and a raw material feed rate of 0.3 kg/hr.The resulting alloy powder was screened with a sieve with 53-μm openingsto collect an alloy powder having a weight-average median diameter D₅₀of 12.8 μm and having a peak of particle-size distribution of about 20μm. The proportion of alloy particles having a diameter of 45 μm or morein the resulting alloy powder was 6%. The proportion of alloy particleshaving a diameter of 5 μm or less was 18%. The QD was 0.60.

The resulting nitrogen-containing alloy was subjected to nitridationunder the same conditions as described in Example 14 to prepare aphosphor (except that the filling rate of the raw material for thephosphor in the firing vessel was set at 26% by volume). The lightemission properties of the resulting phosphor were measured as inExample 14. Table 9 shows the results. Table 8 shows the value of theformula [A] and the temperature change per minute in the heating step.

In addition, 10.16 mg of the resulting nitrogen-containing alloy wasplaced into a boron nitride vessel and heated from room temperature to1,300° C. at a heating rate of 10° C./min under a stream of nitrogen gasat a flow rate of 100 mL/min. A change in weight during heating wasstudied by TG-DTA measurement. FIG. 5 shows the results.

TABLE 7 Analytical result of nitrogen-containing alloy Conditions forprimary nitridation step Oxygen Temperature Rate of weight Metal elementNitrogen content Atmosphere (type of apparatus) (° C.) Time (hr)increase (wt %) content (wt %) content (wt %) (wt %) Example 1 Argoncontaining 2% nitrogen (tubular furnace) 1100 5 4.5 95.7 2.54  2.25Example 2 Argon containing 2% nitrogen (tubular furnace) 1100 5 4.5 95.7— — Example 3 Argon containing 2% nitrogen (tubular furnace) 1050 10 6.294.2 — — Example 4 Argon containing 2% nitrogen (tubular furnace) 105010 6.2 94.2 — — Example 5 Argon containing 7% nitrogen (tubular furnace)1050 10 12.5 88.9 — — Example 6 Argon containing 4% nitrogen (tubularfurnace) 1050 10 8.6 92.1 — — Example 7 Argon containing 5% nitrogen(tubular furnace) 1050 5 6.8 93.6 — — Example 8 Argon containing 5%nitrogen (tubular furnace) 1050 10 8.9 91.8 — — Example 9 Argoncontaining 5% nitrogen (atmosphere 1050 4 5.0 95.2 — — furnace) Example10 Nitrogen (tubular furnace) 1030 8 3.0 97.0 1.1 1.7 Example 11 Mixedgas of nitrogen, argon, and hydrogen 1100 0.05 — — 3.7 1.2 (rotary kiln)Example 12 Argon containing 5% nitrogen (first time) 1050 Heating for —— 10.8 6.5 → nitrogen (second time) (atmosphere furnace) 4 hours twiceExample 13 Argon containing 5% nitrogen (first time) 1050 Heating for —— 15.7 7.4 → nitrogen (second time) (atmosphere furnace) 3 hours threetimes Example 14 Mixed gas of nitrogen, argon and hydrogen 1100 0.05 — —8.9 2.9 (rotary kiln) Example 15 Mixed gas of nitrogen, argon andhydrogen 1100 0.05 — — 8.9 2.9 (rotary kiln) Example 16 Mixed gas ofnitrogen and argon (rotary kiln) 1080 0.05 — — 5.5 2.8 Example 17 Mixedgas of nitrogen and argon (rotary kiln) 1100 0.05 — — 14.4 2.2 Example18 Mixed gas of nitrogen and argon (rotary kiln) 1100 0.05 — — 14.4 2.2Example 19 Mixed gas of nitrogen and argon (rotary kiln) 1100 0.05 — —14.4 2.2 Comparative — — — — 99.7 ≦0.01 0.3 Example 1 Comparative N₂1030 2 2 98.0 0.6 1.4 Example 2

TABLE 8 Conditions for secondary Change in nitridation step temperatureper Value of formula [A] minute (° C./min) Example 1 0.50  ≦2 Example 20.50  ≦2 Example 3 0.50  ≦2 Example 4 0.50  ≦2 Example 5 0.50  ≦2Example 6 0.50  ≦2 Example 7 0.50  ≦2 Example 8 0.50  ≦2 Example 9 0.50 ≦2 Example 10 0.50  ≦2 Example 11 0.50  ≦2 Example 12 0.50  ≦2 Example13 0.50  ≦2 Example 14 0.50  ≦2 Example 15 0.50  ≦2 Example 16 0.50  ≦2Example 17 0.38  ≦2 Example 18 0.50  ≦2 Example 19 0.38  ≦2 Comparative0.50 ≧100 Example 1 Comparative 0.50   ≈80 Example 2

TABLE 9 Relative peak Relative Chromaticity Peak emission emissionbrightness coordinates Nitrogen Oxygen Post-treatment wavelength (nm)intensity (%) (%) x y content (wt %) NI/NP content (wt %) Example 1 None630 92 171 0.635 0.361 — — — Example 2 Washing 634 110  198 0.638 0.359— — — Example 3 None 628 86 161 — — — — — Example 4 Washing and 629 97189 — — — — — classification Example 5 None 630 87 169 — — — — — Example6 None 628 88 174 — — — — — Example 7 None 628 90 176 — — — — — Example8 None 628 86 169 — — — — — Example 9 None 630 92 175 — — — — — Example10 None 628 84 166 — — — — — Washing — — — — — 25.0 0.06 1.0 Example 11None 630 94 182 — — — — — Washing — — — — — 24.0 0.15 1.6 Example 12Washing and 628 98 193 0.630 0.366 23.8 0.45 2.0 classification Example13 Washing and 631 100  189 0.634 0.362 24.0 0.65 1.9 classificationExample 14 None 628 93 185 0.630 0.367 — — — Washing — — — — — 23.7 0.381.8 Example 15 None 627 98 193 0.630 0.366 — — — Washing — — — — — 24.00.37 1.5 Example 16 None 625 73 152 0.624 0.370 — — — Washing — — — — —22.9 0.24 4.1 Example 17 None 625 107  204 0.630 0.367 — — — Example 18Washing and 624 103  197 0.629 0.368 — — — classification Example 19Washing and 627 96 180 0.630 0.366 — — — classification Comparative NoneNot emitted — — — Example 1 Comparative None Not emitted 22.0 0.03 —Example 2

Comparison of Examples 17 and 19 shows that a smaller QD is obtained inExample 17 and that a higher peak emission intensity of the resultingphosphor is observed in Example 17. Hence, a narrow distribution of thealloy powder before the secondary nitridation step tends to lead toimprovement in light emission properties and is thus preferred.

Comparative Example 1

An attempt was made to prepare a phosphor as in Example 1, except thatthe primary nitridation step was not performed, thereby forming a blackblock. Although an attempt was made to measure the light emissionproperties of the resulting alloy block in the same way as in Example 1,light emission was not observed. The nitrogen content, the oxygencontent, the total content of metal elements, and the like of theresulting molten alloy were measured. Tables 7 and 9 show the results.

Furthermore, 13 mg of the alloy powder prepared in the milling stepbefore the primary nitridation step in Example 1 was placed into a boronnitride crucible. TG-DTA measurement of the alloy powder was performedunder the conditions in which heating was performed from roomtemperature to 1,300° C. at a heating rate of 10° C./min under a flow ofnitrogen gas at a flow rate of 100 mL/min. The results demonstrated thatan exotherm and an increase in weight were observed at 1,090° C. to1,100° C. FIG. 10 shows the rate of weight change during the TG-DTAmeasurement. FIG. 10 shows that after the initiation of heating, theweight is instantaneously increased at about 113 minutes (about 1,100°C.). The rate of weight increase at the peak (about 1,100° C.) was1,628%/hour.

Table 8 shows the value of the formula [A] and the temperature changeper minute in the heating step. The temperature change per minute inthis comparative example is significantly larger than those in examples.It is speculated that a rapid exothermic reaction occurs in the furnace.

In Comparative Example 1, the rapid exotherm may cause instantaneousmelting of the alloy powder to reduce the specific surface area, so thatnitridation did not proceed.

Comparative Example 2

A nitrogen-containing alloy was prepared as in Example 1, except thatthe primary nitridation step was performed at 1,030° C. for two hours ina nitrogen flow. Analysis of the resulting nitrogen-containing alloywith regard to its nitrogen content and its oxygen content demonstratedthat the nitrogen content was 0.64% by weight and the oxygen content was1.39% by weight. Furthermore, the rate of weight increase and the totalcontent of metal elements were calculated. Table 7 shows the results.

An attempt was made to prepare a phosphor by subjecting the resultingnitrogen-containing alloy to the secondary nitridation step as inExample 1. Although an attempt was made to evaluate the light emissionproperties as in Example 1, light emission was not observed. Table 9shows the results. The nitrogen content of the resulting phosphor was22% by weight. Table 8 shows the value of the formula [A] and thetemperature change per minute in the heating step. The temperaturechange per minute in this comparative example is significantly largerthan those in examples. It is speculated that a rapid exothermicreaction occurs in the furnace.

In Comparative Example 2, a deterioration in light emission propertiesmay be because a nitridation reaction did not adequately proceed in theprimary nitridation step due to a low temperature and a short period oftime of the primary nitridation step, so that the rate of a nitridationreaction in the secondary nitridation step was not properly controlled.To prepare a high-performance phosphor, therefore, the primarynitridation step should be performed under appropriate conditions.

Example 20

A white light-emitting device shown in FIG. 2( b) was produced with thephosphor (Sr_(0.792)Ca_(0.2)AlSiN₃:Eu_(0.008), serving as a redphosphor, prepared in Example 1 and CaSc₂O₄:Ce_(0.01) (hereinafter, alsoreferred to as “phosphor (A)”) serving as a green phosphor according toa procedure described below.

A blue LED [22] (C460-EZ, manufactured by Cree Incorporation) emittinglight with a wavelength of 455 nm to 460 nm was used as a firstilluminant. The blue LED [22] was bonded to an electrode [27] arrangedat the bottom of a depression of a frame [24] with a silver pasteserving as an adhesive by die bonding. The blue LED [22] was connectedto an electrode [26] of the frame [24] with a gold wire, serving as awire [25], having a diameter of 25 μm.

A phosphor mixture of the two phosphors (the red phosphor and the greenphosphor) was well mixed with a silicone resin (JCR6101UP, manufacturedby Dow Corning Toray Co., Ltd.) in such a manner that the resultingphosphor-silicone resin mixture had a red phosphor content of 0.8% byweight and a green phosphor content of 6.2% by weight. The resultingphosphor-silicone resin mixture (phosphor-containing composition) wasplaced into the depression of the frame [24].

This was maintained at 150° C. for two hours to cure the silicone resin,thus forming a phosphor-containing section [23]. Thereby, asurface-mount white-light-emitting device was produced. In thedescription of this example, reference numerals of components shown inFIG. 2( b) were bracketed.

The resulting surface-mount white-light-emitting device was operated bypassing a current of 20 mA through the blue LED [22] to emit light. Alllight-emitting devices in all examples emitted white light.

The emission spectrum of the resulting surface-mountwhite-light-emitting device was measured. FIG. 13 shows the results.Table 10 shows values of various light emission properties (totalluminous flux, optical output, chromaticity coordinates, colortemperature, color deviation, color rendering index) calculated from theresulting emission spectrum. In Table 10, Tcp represents a correlatedcolor temperature (unit: K), and Duv represents color deviation.

The combination of the phosphor of the present invention and any greenphosphor results in a light-emitting device having high color renderingproperties.

TABLE 10 Total luminous flux 3.9 (lm) Optical output 12.9 (mW)Chromaticity x 0.346 coordinates y 0.364 Tcp 5000 Duv 5.8 Ra 89 R01 89R02 96 R03 96 R04 84 R05 88 R06 94 R07 88 R08 77 R09 43 R10 91 R11 86R12 63 R13 92 R14 98 R15 83

Reference Example 2 Production of Alloy

Raw material metals were weighed in such a manner that the compositionratio of metal elements, i.e., the ratio (molar ratio) of Al to Si, was1:1. The raw material metals were charged into a graphite crucible andmelted in an argon atmosphere with a high-frequency induction meltingfurnace. The molten metal mixture was poured from the crucible into amold and then solidified, whereby an alloy (a mother alloy) in which thecomposition ratio of the metal elements, i.e., the ratio of Al to Si,was 1:1, was obtained.

The mother alloy and other raw material metals were weighed in such amanner that the ratio of Eu to Sr to Ca to Al to Si was0.008:0.792:0.2:1:1 (molar ratio). After a furnace was evacuated to5×10⁻² Pa, the evacuation of the furnace was stopped, and argon was thenintroduced into the furnace until the pressure in the furnace reached apredetermined value. The mother alloy was melted in a calcia crucibleplaced in the furnace. Sr, Eu, and Ca, which are the raw materialmetals, were added thereto. After all these components were melted intoa mixture and the molten mixture was observed to have been agitated byan induction current, the molten mixture was poured from the crucibleinto a water-cooled copper mold (a plate shape with a thickness of 40mm) and then solidified.

A 40-mm-thick plate of the resulting alloy was analyzed with regard toits composition by an ICP technique. About 10 g of a sample was takenfrom a portion close to the center of gravity of the plate and about 10g of a sample was taken from an end portion of the plate. The elementalanalysis of the samples using the ICP technique determined that thesamples had substantially the same composition as the alloy plateprepared in Example 1 within the scope of analytical precision.Therefore, Eu and the other elements seemed to be uniformly distributed.

The resulting alloy had an X-ray powder diffraction pattern similar tothat of Sr(Si_(0.5)Al_(0.5))₂ and therefore was determined to be anAlB₂-type intermetallic compound referred to as an alkaline-earthsilicide.

The resulting alloy was milled with an alumina mortar in a nitrogenatmosphere (containing 4%, oxygen) for 60 minutes. Undersize particlesof the alloy that passed through a sieve with 53-μm openings werecollected to obtain an alloy powder. Hereinafter, this alloy powder isreferred to as an “alloy powder prepared in Reference Example 2”.

Nitridation Treatment

Into a boron nitride crucible (having an inner diameter of 54 mm), 10 gof the alloy powder prepared as above was placed. The boron nitridecrucible was set in a hot isostatic press (HIP). The press was evacuatedto 5×10⁻¹ Pa. The alloy powder was heated to 300° C. The evacuation wascontinued for one hour at 300° C. Nitrogen was charged into the press insuch a manner that the pressure in the press was increased to 1 MPa. Thealloy powder was cooled. The pressure in the press was reduced to 0.1MPa. Nitrogen was introduced into the press again in such a manner thatthe pressure in the press was increased to 1 MPa. This procedure wasrepeated twice. Nitrogen was introduced into the press in such a mannerthat the pressure in the press was increased to 50 MPa before initiationof heating. The alloy powder was heated until the temperature in thefurnace reached 950° C. at a heating rate of 600° C./hr while theinternal pressure was increased to about 135 MPa at a pressurizationrate of about 50 MPa/hr. The temperature in the furnace is increasedfrom 950° C. to 1,100° C. at a heating rate of 66.7° C./hr (about 1.11°C./min) while the internal pressure was increased from 135 MPa to 160MPa. Heating and pressurization were performed in such a manner that thetemperature in the furnace was increased to 1,850° C. at a heating rateof about 600° C./hr and the internal pressure was increased to 180 MPa.This temperature and this pressure were maintained for one hour. Theresulting fired product was milled, washed, classified to prepare aphosphor having a weight-average median diameter D₅₀ of 8 μm.

The characterization of the phosphor by X-ray powder diffraction showedthe presence of an orthorhombic crystal isomorphic to CaAlSiN₃. Thetarget composition of the phosphor wasEu_(0.008)Sr_(0.792)Ca_(0.2)AlSiN₃. Hereinafter, this phosphor isreferred to as a “phosphor in Reference Example 2”.

Example 21

Nitridation treatment was performed under the same conditions asdescribed in Reference Example 2, except that a mixture of 18.6 g of thealloy powder prepared in Reference Example 2 and 10 g of the phosphor inReference Example 2 was placed into a boron nitride crucible, therebypreparing a phosphor having the same structure as the phosphor inReference Example 2. The emission spectrum of this phosphor was measuredby the foregoing method with an excitation wavelength of 465 nm. Thepeak emission intensity and the brightness were determined from theresulting emission spectrum with respect to 100% of the phosphorprepared in Reference Example 1. Table 11 shows the results. Table 11also shows the value of the formula [A] and the temperature change perminute in the heating step.

Example 22

Nitridation treatment was performed under the same conditions asdescribed in Reference Example 2, except that a mixture of 22.9 g of thealloy powder prepared in Reference Example 2 and 5.7 g of the phosphorin Reference Example 2 was placed into a boron nitride crucible, therebypreparing a phosphor having the same structure as the phosphor inReference Example 2. The emission spectrum of this phosphor was measuredby the foregoing method with an excitation wavelength of 465 nm. Thepeak emission intensity and the brightness were determined from theresulting emission spectrum with respect to 100% of the phosphorprepared in Reference Example 1. Table 11 shows the results. Table 11also shows the value of the formula [A] and the temperature change perminute in the heating step.

Example 23

Nitridation treatment was performed under the same conditions asdescribed in Reference Example 2, except that a mixture of 28.5 g of thealloy powder prepared in Reference Example 2 and 15.3 g of the phosphorin Reference Example 2 was placed into a boron nitride crucible, therebypreparing a phosphor having the same structure as the phosphor inReference Example 2. The emission spectrum of this phosphor was measuredby the foregoing method with an excitation wavelength of 465 nm. Thepeak emission intensity and the brightness were determined from theresulting emission spectrum with respect to 100% of the phosphorprepared in Reference Example 1. Table 11 shows the results. Table 11also shows the value of the formula [A] and the temperature change perminute in the heating step.

Example 24

Nitridation treatment was performed under the same conditions asdescribed in Reference Example 2, except that a mixture of 25.7 g of thealloy powder prepared in Reference Example 2 and 2.9 g of the phosphorin Reference Example 2 was placed into a boron nitride crucible, therebypreparing a phosphor having the same structure as the phosphor inReference Example 2. The emission spectrum of this phosphor was measuredby the foregoing method with an excitation wavelength of 465 nm. Thepeak emission intensity and the brightness were determined from theresulting emission spectrum with respect to 100% of the phosphorprepared in Reference Example 1. Table 11 shows the results. Table 11also shows the value of the formula [A] and the temperature change perminute in the heating step.

Example 25

Nitridation treatment was performed under the same conditions asdescribed in Reference Example 2, except that a mixture of 27.2 g of thealloy powder prepared in Reference Example 2 and 1.4 g of the phosphorin Reference Example 2 was placed into a boron nitride crucible, therebypreparing a phosphor having the same structure as the phosphor inReference Example 2. The emission spectrum of this phosphor was measuredby the foregoing method with an excitation wavelength of 465 nm. Thepeak emission intensity and the brightness were determined from theresulting emission spectrum with respect to 100% of the phosphorprepared in Reference Example 1. Table 11 shows the results. Table 11also shows the value of the formula [A] and the temperature change perminute in the heating step.

Example 30

Nitridation treatment was performed under the same conditions asdescribed in Reference Example 2, except that 18.6 g of the alloy powderprepared in Reference Example 2 was placed into a boron nitridecrucible. The emission spectrum of the resulting phosphor was measuredby the foregoing method with an excitation wavelength of 465 nm. Thepeak emission intensity and the brightness were determined from theresulting emission spectrum with respect to 100% of the phosphorprepared in Reference Example 1. Table 11 shows the results. Table 11also shows the value of the formula [A] and the temperature change perminute in the heating step.

Comparative Example 4

Nitridation treatment was performed under the same conditions asdescribed in Reference Example 2, except that 28.5 g of the alloy powderprepared in Reference Example 2 was placed into a boron nitridecrucible, thereby preparing a black block with a slightly reddishsurface, which did not emit light. Table 11 also shows the value of theformula [A] and the temperature change per minute in the heating step.

TABLE 11 Mixing ratio of Mixing ratio of material (wt %) material (g)Light emission properties of phosphor Alloy powder Phosphor Alloy powderPeak Temperature prepared in in prepared in Phosphor in emission changeper Reference Reference Reference Reference wavelength Peak emissionValue of minute Example 1 Example 1 Example 1 Example 1 (nm) intensity(%) Brightness (%) formula [A] (° C./min) Example 21 65 35 18.6 10 62799 187 0.42 ≦10 Example 22 80 20 22.9 5.7 627 97 186 0.42 ≦10 Example 2365 35 28.5 15.3 626 100  188 0.52 ≦10 Example 24 90 10 25.7 2.9 626 91177 0.42 ≦10 Example 25 95 5 27.2 1.4 626 88 172 0.42 ≦10 Example 30 1000 18.6 0 627 86 165 0.32 ≦10 Comparative 100 0 28.5 0 — Not emitted Notemitted 0.42 +100 Example 4

The results described above demonstrate as follows.

In the case of the production of the phosphor from the alloy, in somecases, the phosphor is not prepared when a large amount of the alloy isplaced into the reaction vessel (Comparative Example 4). Furthermore, inthe case where the phosphor is not mixed, the light emission propertiesof the phosphor tend to be reduced compared with those of the case wherethe phosphor is mixed (Example 30).

In contrast, in the case where nitridation treatment is performed in thepresence of the nitride material, the phosphor having excellent lightemission properties is obtained even when a large amount of the alloy isplaced into the reaction vessel (Examples 21 to 25).

Example 26

An alloy for a phosphor precursor was prepared under the same conditionsas described in Example 1. The resulting plate-shaped alloy for aphosphor precursor had substantially the same composition as the alloyin Example 1 within the scope of analytical precision.

The plate-shaped alloy was milled with an alumina mortar in a nitrogenflow to form an alloy powder with a weight-average median diameter D₅₀of 20.0 μm.

The melting point of the alloy powder was measured by the methoddescribed above under argon flow. The melting initiation temperature wasabout 1,078° C., and the melting point was 1,121° C.

Into a boron nitride crucible (having an inner diameter of 54 mm), 10 gof the resulting alloy powder was placed. The boron nitride crucible wasset in a hot isostatic press (HIP). The press was evacuated to 5×10⁻¹Pa. The alloy powder was heated to 300° C. The evacuation was continuedfor one hour at 300° C. Nitrogen was charged into the press in such amanner that the pressure in the press was increased to 1 MPa. The alloypowder was cooled. The pressure in the press was reduced to 0.1 MPa.Nitrogen was introduced into the press again in such a manner that thepressure in the press was increased to 1 MPa. This procedure wasrepeated twice. Nitrogen was introduced into the press in such a mannerthat the pressure in the press was increased to 50 MPa before initiationof heating. The alloy powder was heated until the temperature in thefurnace reached 1,000° C. at a heating rate of 600° C./hr while theinternal pressure was increased to about 135 MPa at a pressurizationrate of about 50 MPa/hr. The temperature in the furnace is increasedfrom 1,000° C. to 1,200° C. at a heating rate of 66.7° C./hr while theinternal pressure was increased from 135 MPa to 160 MPa. Heating andpressurization were performed in such a manner that the temperature inthe furnace was increased to 1,850° C. at a heating rate of 600° C./hrand the internal pressure was increased to 190 MPa. This temperature andthis pressure were maintained for one hour to prepare a phosphor.

The characterization of the phosphor by X-ray powder diffraction showedthe presence of an orthorhombic crystal isomorphic to CaAlSiN₃.

In Example 26, the heating rate was 1.11° C./min in the temperaturerange from the temperature (1,021° C.) 100° C. lower than the meltingpoint (1,121° C.) of the alloy to the temperature (1,091° C.) 30° C.lower than the melting point of the alloy.

The emission spectrum of the resulting phosphor was measured by theforegoing method with an excitation wavelength of 465 nm. Table 12 showsthe results. Table 12 also shows the value of the formula [A] and thetemperature change per minute in the heating step.

Example 31

Nitridation treatment was performed as in Example 26, except that in thenitridation treatment in the HIP, the temperature in the furnace wasincreased to 950° C. (internal pressure: 130 MPa) at a heating rate of600° C./hr, maintained at 950° C. for 2.5 hours, and then increased to1,850° C. (internal pressure: 190 MPa) at a heating rate of 600° C./hr,thereby preparing a phosphor.

In Comparative Example 5, the heating rate was 10° C./min in thetemperature range from the temperature (1,021° C.) 100° C. lower thanthe melting point (1,121° C.) of the alloy to the temperature (1,091°C.) 30° C. lower than the melting point of the alloy.

The light emission properties of the resulting phosphor were measured asin Example 1. Table 12 shows the results. Table 12 also shows the valueof the formula [A] and the temperature change per minute in the heatingstep.

Example 32

Nitridation treatment was performed as in Example 26, except that in thenitridation treatment in the HIP, the temperature in the furnace wasincreased to 1,850° C. (internal pressure: 190 MPa) at a heating rate of570° C./hr, thereby preparing a phosphor.

In Comparative Example 6, the heating rate was 9.5° C./min in thetemperature range from the temperature (1,021° C.) 100° C. lower thanthe melting point (1,121° C.) of the alloy to the temperature (1,091°C.) 30° C. lower than the melting point of the alloy.

The light emission properties of the resulting phosphor were measured asin Example 26. Table 12 shows the results. Table 12 also shows the valueof the formula [A] and the temperature change per minute in the heatingstep.

TABLE 12 Peak Temperature Heating emission Bright- Value of change perrate* wavelength ness formula minute (° C./min) (nm) (%) [A] (° C./min)Example 26 1.11 627 194 0.20  ≦3 Example 31 10 626 172 0.20 ≦20 Example32 9.5 624 131 0.20 ≦20 *The heating rate indicates a heating rate inthe temperature range from the temperature (1,021° C.) 100° C. lowerthan the melting point (1,121° C.) of the alloy to the temperature(1,091° C.) 30° C. lower than the melting point of the alloy.

Table 12 shows that a low heating rate in the temperature range from thetemperature (1,021° C.) 100° C. lower than the melting point (1,121° C.)of the alloy to the temperature (1,091° C.) 30° C. lower than themelting point of the alloy results in improvement in the brightness ofthe resulting phosphor (Example 26).

It is speculated that the reason for this is that in Example 26, inwhich the heating rate was low in the specific temperature range, theaccumulation of the heat of reaction due to nitridation was reducedcompared with Examples 31 and 32, in which the heating rates were high.

Furthermore, the results of Examples 31 and 32 demonstrate that in thecase of a low value of the formula [A], the phosphors were produced evenif the requirements 1) to 4) described above were not satisfied.

Example 27 Production of Alloy

An alloy for a phosphor precursor was prepared under the same conditionsas described in Example 1. The resulting plate-shaped alloy for aphosphor precursor had substantially the same composition as the alloyin Example 1 within the scope of analytical precision.

Atomization of Alloy

The resulting plate-shaped alloy was atomized with an ultrasmall gasatomizer having a structure shown in FIG. 4.

Specifically, the plate-shaped alloy was placed into an aluminum oxidecrucible. The plate-shaped alloy was heated to 1,000° C. in a meltingchamber in vacuum and then melted at about 1,530° C. in an argonatmosphere. The melting chamber 101 was pressurized to a gauge pressureof about 0.05 MPa. The molten alloy was poured from the aluminum oxideinjection nozzles 104 with an internal diameter of 2 mm into theinjection chamber 105 (atmospheric pressure) filled with nitrogen.Simultaneously, jet blasts of an atomization gas (nitrogen) weredelivered to the molten alloy at a blast pressure of 50 kgf/cm² (4.9MPa), thereby atomizing droplets. The resulting powder collected in thecollection chamber 106 (atmospheric pressure) filled with nitrogen wasscreened with a sieve with 53-μm openings, thereby obtaining an alloypowder.

Table 13 shows the angle of repose, the collapse angle, the differenceangle, the tap density, the weight-average median diameter D₅₀, theoxygen content, and the carbon content of the resulting alloy powder.

Furthermore, the optical micrograph (FIG. 14) of the alloy powder showedthat most of the resulting alloy particles were spherical.

Production of Phosphor

Into a boron nitride crucible, 32 g of the alloy powder was placed. Theboron nitride crucible was set in a hot isostatic press (HIP). The presswas evacuated to 5×10⁻¹ Pa. The alloy powder was heated to 300° C. Theevacuation was continued for one hour at 300° C. Nitrogen was chargedinto the press in such a manner that the pressure in the press wasincreased to 1 MPa. The alloy powder was cooled. The pressure in thepress was reduced to 0.1 MPa. Nitrogen was introduced into the pressagain in such a manner that the pressure in the press was increased to 1MPa. This procedure was repeated twice. Nitrogen was introduced into thepress in such a manner that the pressure in the press was increased to50 MPa before initiation of heating. Heating and pressurization wereperformed in such a manner that the temperature in the furnace wasincreased to 1,800° C. and the internal pressure was increased to 180MPa over a period of three hours. This state was maintained for one hourto prepare a phosphor.

The characterization of the phosphor by X-ray powder diffraction showedthe presence of an orthorhombic crystal isomorphic to CaAlSiN₃.

The emission spectrum of the resulting phosphor was measured by theforegoing method with an excitation wavelength of 465 nm. The relativebrightness and peak emission wavelength were determined. Table 13 showsthe results. Table 13 also shows the value of the formula [A] and thetemperature change per minute in the heating step.

Example 28

A phosphor was prepared as in Example 27, except that an alloy powdercollected with the cyclone 107 was screened with a sieve having 53-1 μmopenings to obtain an alloy powder.

Table 13 shows the measurement results of powder characteristics and thelike of the alloy powder and the relative brightness and the peakemission wavelength of the phosphor. Table 13 also shows the value ofthe formula [A] and the temperature change per minute in the heatingstep.

Example 29

A phosphor was prepared as in Example 28, except that the alloy powderwas prepared with the gas atomizer having the crucible 103 and theinjection nozzles 104 composed of graphite.

Table 13 shows the measurement results of powder characteristics and thelike of the alloy powder and the relative brightness and the peakemission wavelength of the phosphor. Table 13 also shows the value ofthe formula [A] and the temperature change per minute in the heatingstep.

Comparative Example 7

An alloy cast by the same method as in Example 27 was not atomized withthe gas atomizer but milled with an alumina mortar in a nitrogenatmosphere (containing 4% or less oxygen) for three hours. Undersizeparticles of the alloy that passed through a sieve with 53-μm openingswere collected.

The optical micrograph (FIG. 15) of the resulting alloy powder showedthat the alloy particles were not spherical but irregular.

Table 13 shows the measurement results of powder characteristics and thelike of the alloy powder. Table 13 also shows the value of the formula[A] and the temperature change per minute in the heating step.

Although an attempt was made to prepare a phosphor by treating theresulting alloy powder in a hot isostatic press (HIP) as in Example 27,a black block was obtained. The black block did not emit light at 465-nmexcitation.

TABLE 13 Alloy powder for phosphor precursor Weight- Angle averagePhosphor Value Temperature of Collapse Tap median Oxygen Carbon Peak ofchange per repose angle Difference density diameter content contentemission formula minute (°) (°) angle (°) (g/mL) D50 (mm) (wt %) (wt %)Brightness wavelength [A] (° C./min) Example 27 32.1 14.3 17.8 2.13 38.00.86 0.05 169 626 0.44 ≦20 Example 28 32 14.2 17.8 2.07 22.8 0.86 0.05174 625 0.44 ≦20 Example 29 32.2 14.5 17.7 2.10 19.5 0.30 0.12 122 6230.44 ≦20 Comparative 51.3 29.9 21.4 1.86 15.6 0.20 ≦0.03 — — 0.44 ≧80Example 7

As is clear from the above results, the present invention provides aphosphor with high brightness is produced using an alloy powder forphosphor precursor with low impurities and high flowability.

It is speculated that in Example 29, the phosphor had a brightness lowerthan those in Examples 27 and 28 because of contamination with carbonfrom the graphite crucible and nozzles.

The present application is based on a Japanese patent application(Japanese Patent Application No. 2006-140557) filed on May 19, 2006; aJapanese patent application (Japanese Patent Application No.2006-153632) filed on Jun. 1, 2006; a Japanese patent application(Japanese Patent Application No. 2006-184667) filed on Jul. 4, 2006; anda Japanese patent application (Japanese Patent Application No.2006-267714) filed on Sep. 29, 2006. These applications are fullyincorporated herein by reference.

1-5. (canceled)
 6. A method for producing a phosphor, comprising a stepof heating a raw material for the phosphor under a nitrogen-containingatmosphere, wherein an alloy for a phosphor precursor is used as thewhole or part of the raw material for the phosphor, and wherein themethod satisfies at least one of requirements 1) to 4): 1) the whole orpart of the alloy for a phosphor precursor is a nitrogen-containingalloy having a total content of metal elements of 97% by weight or less;2) the heating rate is set at 9° C./min or less in the temperature rangefrom a temperature 100° C. lower than the melting point of the alloy fora phosphor precursor to a temperature 30° C. lower than the meltingpoint of the alloy for a phosphor precursor; 3) a nitride or anoxynitride containing one or two or more metal elements constituting thephosphor is used as the raw material for the phosphor together with thealloy for a phosphor precursor; and 4) a powder of the alloy for aphosphor precursor is used as the alloy for a phosphor precursor, thepowder having an angle of repose of 45° or less.
 7. The method forproducing a phosphor according to claim 6, wherein thenitrogen-containing alloy has a nitrogen content of 0.8% by weight to27% by weight.
 8. The method for producing a phosphor according to claim6 or 7, further comprising a step (hereinafter, referred to as a“primary nitridation step”) of heating the alloy for a phosphorprecursor under a nitrogen-containing atmosphere to prepare thenitrogen-containing alloy.
 9. The method for producing a phosphoraccording to claim 6, wherein the nitrogen-containing alloy satisfiesthe formula [7]:0.03≦NI/NP≦0.9  [7] wherein in the formula [7], NI represents thenitrogen content (% by weight) of the nitrogen-containing alloy; and NPrepresents the nitrogen content (% by weight) of the phosphor produced.10. The method for producing a phosphor according to claim 6, whereinthe step (hereinafter, referred to as a “secondary nitridation step”) ofheating the raw material for the phosphor, the whole or part of the rawmaterial being consisted of the nitrogen-containing alloy under thenitrogen-containing atmosphere is performed at a temperature equal to orhigher than a temperature 300° C. higher than the melting point of thenitrogen-containing alloy.
 11. The method for producing a phosphoraccording to claim 6, further comprising a step of cooling thenitrogen-containing alloy to a temperature equal to or lower than atemperature 100° C. lower than the melting point of thenitrogen-containing alloy before the secondary nitridation step.
 12. Themethod for producing a phosphor according to claim 6, further comprisinga step of milling the nitrogen-containing alloy before the secondarynitridation step.
 13. The method for producing a phosphor according toclaim 6, wherein the alloy for a phosphor precursor has a weight-averagemedian diameter D₅₀ of 100 μm or less.
 14. The method for producing aphosphor according to claim 6, wherein the raw material for the phosphorcontains 1% by weight or more of a nitride or an oxynitride containingone or two or more metal elements constituting the phosphor togetherwith the alloy for a phosphor precursor.
 15. The method for producing aphosphor according to claim 6, wherein the alloy for a phosphorprecursor has a tap density of 1.9 g/mL or more. 16-21. (canceled) 22.The method for producing a phosphor according to claim 6, wherein thephosphor contains a tetravalent metal element M⁴ containing at least Siand contains one or more metal elements other than Si.
 23. The methodfor producing a phosphor according to claim 22, wherein the phosphorcontains an activating element M¹, a divalent metal element M², and thetetravalent metal element M⁴ containing at least Si.
 24. The method forproducing a phosphor according to claim 23, wherein the phosphorcontains an alkaline-earth metal element serving as the divalent metalelement M². 25-46. (canceled)
 47. A method for producing a phosphoraccording to claim 6, wherein the whole or part of the alloy for aphosphor precursor is a nitrogen-containing alloy having a nitrogencontent of 10% by weight or more.